Exemplo n.º 1
0
PreservedAnalyses
PassManager<LazyCallGraph::SCC, CGSCCAnalysisManager, LazyCallGraph &,
            CGSCCUpdateResult &>::run(LazyCallGraph::SCC &InitialC,
                                      CGSCCAnalysisManager &AM,
                                      LazyCallGraph &G, CGSCCUpdateResult &UR) {
  PreservedAnalyses PA = PreservedAnalyses::all();

  if (DebugLogging)
    dbgs() << "Starting CGSCC pass manager run.\n";

  // The SCC may be refined while we are running passes over it, so set up
  // a pointer that we can update.
  LazyCallGraph::SCC *C = &InitialC;

  for (auto &Pass : Passes) {
    if (DebugLogging)
      dbgs() << "Running pass: "******" on " << *C << "\n";

    PreservedAnalyses PassPA = Pass->run(*C, AM, G, UR);

    // Update the SCC if necessary.
    C = UR.UpdatedC ? UR.UpdatedC : C;

    // Check that we didn't miss any update scenario.
    assert(!UR.InvalidatedSCCs.count(C) && "Processing an invalid SCC!");
    assert(C->begin() != C->end() && "Cannot have an empty SCC!");

    // Update the analysis manager as each pass runs and potentially
    // invalidates analyses.
    AM.invalidate(*C, PassPA);

    // Finally, we intersect the final preserved analyses to compute the
    // aggregate preserved set for this pass manager.
    PA.intersect(std::move(PassPA));

    // FIXME: Historically, the pass managers all called the LLVM context's
    // yield function here. We don't have a generic way to acquire the
    // context and it isn't yet clear what the right pattern is for yielding
    // in the new pass manager so it is currently omitted.
    // ...getContext().yield();
  }

  // Invaliadtion was handled after each pass in the above loop for the current
  // SCC. Therefore, the remaining analysis results in the AnalysisManager are
  // preserved. We mark this with a set so that we don't need to inspect each
  // one individually.
  PA.preserve<AllAnalysesOn<LazyCallGraph::SCC>>();

  if (DebugLogging)
    dbgs() << "Finished CGSCC pass manager run.\n";

  return PA;
}
Exemplo n.º 2
0
PreservedAnalyses ArgumentPromotionPass::run(LazyCallGraph::SCC &C,
                                             CGSCCAnalysisManager &AM,
                                             LazyCallGraph &CG,
                                             CGSCCUpdateResult &UR) {
  bool Changed = false, LocalChange;

  // Iterate until we stop promoting from this SCC.
  do {
    LocalChange = false;

    for (LazyCallGraph::Node &N : C) {
      Function &OldF = N.getFunction();

      FunctionAnalysisManager &FAM =
          AM.getResult<FunctionAnalysisManagerCGSCCProxy>(C, CG).getManager();
      // FIXME: This lambda must only be used with this function. We should
      // skip the lambda and just get the AA results directly.
      auto AARGetter = [&](Function &F) -> AAResults & {
        assert(&F == &OldF && "Called with an unexpected function!");
        return FAM.getResult<AAManager>(F);
      };

      Function *NewF = promoteArguments(&OldF, AARGetter, MaxElements, None);
      if (!NewF)
        continue;
      LocalChange = true;

      // Directly substitute the functions in the call graph. Note that this
      // requires the old function to be completely dead and completely
      // replaced by the new function. It does no call graph updates, it merely
      // swaps out the particular function mapped to a particular node in the
      // graph.
      C.getOuterRefSCC().replaceNodeFunction(N, *NewF);
      OldF.eraseFromParent();
    }

    Changed |= LocalChange;
  } while (LocalChange);

  if (!Changed)
    return PreservedAnalyses::all();

  return PreservedAnalyses::none();
}
Exemplo n.º 3
0
FunctionAnalysisManagerCGSCCProxy::Result
FunctionAnalysisManagerCGSCCProxy::run(LazyCallGraph::SCC &C,
                                       CGSCCAnalysisManager &AM,
                                       LazyCallGraph &CG) {
  // Collect the FunctionAnalysisManager from the Module layer and use that to
  // build the proxy result.
  //
  // This allows us to rely on the FunctionAnalysisMangaerModuleProxy to
  // invalidate the function analyses.
  auto &MAM = AM.getResult<ModuleAnalysisManagerCGSCCProxy>(C, CG).getManager();
  Module &M = *C.begin()->getFunction().getParent();
  auto *FAMProxy = MAM.getCachedResult<FunctionAnalysisManagerModuleProxy>(M);
  assert(FAMProxy && "The CGSCC pass manager requires that the FAM module "
                     "proxy is run on the module prior to entering the CGSCC "
                     "walk.");

  // Note that we special-case invalidation handling of this proxy in the CGSCC
  // analysis manager's Module proxy. This avoids the need to do anything
  // special here to recompute all of this if ever the FAM's module proxy goes
  // away.
  return Result(FAMProxy->getManager());
}
Exemplo n.º 4
0
PreservedAnalyses
PassManager<LazyCallGraph::SCC, CGSCCAnalysisManager, LazyCallGraph &,
            CGSCCUpdateResult &>::run(LazyCallGraph::SCC &InitialC,
                                      CGSCCAnalysisManager &AM,
                                      LazyCallGraph &G, CGSCCUpdateResult &UR) {
  // Request PassInstrumentation from analysis manager, will use it to run
  // instrumenting callbacks for the passes later.
  PassInstrumentation PI =
      AM.getResult<PassInstrumentationAnalysis>(InitialC, G);

  PreservedAnalyses PA = PreservedAnalyses::all();

  if (DebugLogging)
    dbgs() << "Starting CGSCC pass manager run.\n";

  // The SCC may be refined while we are running passes over it, so set up
  // a pointer that we can update.
  LazyCallGraph::SCC *C = &InitialC;

  for (auto &Pass : Passes) {
    if (DebugLogging)
      dbgs() << "Running pass: "******" on " << *C << "\n";

    // Check the PassInstrumentation's BeforePass callbacks before running the
    // pass, skip its execution completely if asked to (callback returns false).
    if (!PI.runBeforePass(*Pass, *C))
      continue;

    PreservedAnalyses PassPA = Pass->run(*C, AM, G, UR);

    if (UR.InvalidatedSCCs.count(C))
      PI.runAfterPassInvalidated<LazyCallGraph::SCC>(*Pass);
    else
      PI.runAfterPass<LazyCallGraph::SCC>(*Pass, *C);

    // Update the SCC if necessary.
    C = UR.UpdatedC ? UR.UpdatedC : C;

    // If the CGSCC pass wasn't able to provide a valid updated SCC, the
    // current SCC may simply need to be skipped if invalid.
    if (UR.InvalidatedSCCs.count(C)) {
      LLVM_DEBUG(dbgs() << "Skipping invalidated root or island SCC!\n");
      break;
    }
    // Check that we didn't miss any update scenario.
    assert(C->begin() != C->end() && "Cannot have an empty SCC!");

    // Update the analysis manager as each pass runs and potentially
    // invalidates analyses.
    AM.invalidate(*C, PassPA);

    // Finally, we intersect the final preserved analyses to compute the
    // aggregate preserved set for this pass manager.
    PA.intersect(std::move(PassPA));

    // FIXME: Historically, the pass managers all called the LLVM context's
    // yield function here. We don't have a generic way to acquire the
    // context and it isn't yet clear what the right pattern is for yielding
    // in the new pass manager so it is currently omitted.
    // ...getContext().yield();
  }

  // Invalidation was handled after each pass in the above loop for the current
  // SCC. Therefore, the remaining analysis results in the AnalysisManager are
  // preserved. We mark this with a set so that we don't need to inspect each
  // one individually.
  PA.preserveSet<AllAnalysesOn<LazyCallGraph::SCC>>();

  if (DebugLogging)
    dbgs() << "Finished CGSCC pass manager run.\n";

  return PA;
}
Exemplo n.º 5
0
PreservedAnalyses InlinerPass::run(LazyCallGraph::SCC &InitialC,
                                   CGSCCAnalysisManager &AM, LazyCallGraph &CG,
                                   CGSCCUpdateResult &UR) {
  const ModuleAnalysisManager &MAM =
      AM.getResult<ModuleAnalysisManagerCGSCCProxy>(InitialC, CG).getManager();
  bool Changed = false;

  assert(InitialC.size() > 0 && "Cannot handle an empty SCC!");
  Module &M = *InitialC.begin()->getFunction().getParent();
  ProfileSummaryInfo *PSI = MAM.getCachedResult<ProfileSummaryAnalysis>(M);

  if (!ImportedFunctionsStats &&
      InlinerFunctionImportStats != InlinerFunctionImportStatsOpts::No) {
    ImportedFunctionsStats =
        llvm::make_unique<ImportedFunctionsInliningStatistics>();
    ImportedFunctionsStats->setModuleInfo(M);
  }

  // We use a single common worklist for calls across the entire SCC. We
  // process these in-order and append new calls introduced during inlining to
  // the end.
  //
  // Note that this particular order of processing is actually critical to
  // avoid very bad behaviors. Consider *highly connected* call graphs where
  // each function contains a small amonut of code and a couple of calls to
  // other functions. Because the LLVM inliner is fundamentally a bottom-up
  // inliner, it can handle gracefully the fact that these all appear to be
  // reasonable inlining candidates as it will flatten things until they become
  // too big to inline, and then move on and flatten another batch.
  //
  // However, when processing call edges *within* an SCC we cannot rely on this
  // bottom-up behavior. As a consequence, with heavily connected *SCCs* of
  // functions we can end up incrementally inlining N calls into each of
  // N functions because each incremental inlining decision looks good and we
  // don't have a topological ordering to prevent explosions.
  //
  // To compensate for this, we don't process transitive edges made immediate
  // by inlining until we've done one pass of inlining across the entire SCC.
  // Large, highly connected SCCs still lead to some amount of code bloat in
  // this model, but it is uniformly spread across all the functions in the SCC
  // and eventually they all become too large to inline, rather than
  // incrementally maknig a single function grow in a super linear fashion.
  SmallVector<std::pair<CallSite, int>, 16> Calls;

  FunctionAnalysisManager &FAM =
      AM.getResult<FunctionAnalysisManagerCGSCCProxy>(InitialC, CG)
          .getManager();

  // Populate the initial list of calls in this SCC.
  for (auto &N : InitialC) {
    auto &ORE =
        FAM.getResult<OptimizationRemarkEmitterAnalysis>(N.getFunction());
    // We want to generally process call sites top-down in order for
    // simplifications stemming from replacing the call with the returned value
    // after inlining to be visible to subsequent inlining decisions.
    // FIXME: Using instructions sequence is a really bad way to do this.
    // Instead we should do an actual RPO walk of the function body.
    for (Instruction &I : instructions(N.getFunction()))
      if (auto CS = CallSite(&I))
        if (Function *Callee = CS.getCalledFunction()) {
          if (!Callee->isDeclaration())
            Calls.push_back({CS, -1});
          else if (!isa<IntrinsicInst>(I)) {
            using namespace ore;
            ORE.emit([&]() {
              return OptimizationRemarkMissed(DEBUG_TYPE, "NoDefinition", &I)
                     << NV("Callee", Callee) << " will not be inlined into "
                     << NV("Caller", CS.getCaller())
                     << " because its definition is unavailable"
                     << setIsVerbose();
            });
          }
        }
  }
  if (Calls.empty())
    return PreservedAnalyses::all();

  // Capture updatable variables for the current SCC and RefSCC.
  auto *C = &InitialC;
  auto *RC = &C->getOuterRefSCC();

  // When inlining a callee produces new call sites, we want to keep track of
  // the fact that they were inlined from the callee.  This allows us to avoid
  // infinite inlining in some obscure cases.  To represent this, we use an
  // index into the InlineHistory vector.
  SmallVector<std::pair<Function *, int>, 16> InlineHistory;

  // Track a set vector of inlined callees so that we can augment the caller
  // with all of their edges in the call graph before pruning out the ones that
  // got simplified away.
  SmallSetVector<Function *, 4> InlinedCallees;

  // Track the dead functions to delete once finished with inlining calls. We
  // defer deleting these to make it easier to handle the call graph updates.
  SmallVector<Function *, 4> DeadFunctions;

  // Loop forward over all of the calls. Note that we cannot cache the size as
  // inlining can introduce new calls that need to be processed.
  for (int i = 0; i < (int)Calls.size(); ++i) {
    // We expect the calls to typically be batched with sequences of calls that
    // have the same caller, so we first set up some shared infrastructure for
    // this caller. We also do any pruning we can at this layer on the caller
    // alone.
    Function &F = *Calls[i].first.getCaller();
    LazyCallGraph::Node &N = *CG.lookup(F);
    if (CG.lookupSCC(N) != C)
      continue;
    if (F.hasFnAttribute(Attribute::OptimizeNone))
      continue;

    LLVM_DEBUG(dbgs() << "Inlining calls in: " << F.getName() << "\n");

    // Get a FunctionAnalysisManager via a proxy for this particular node. We
    // do this each time we visit a node as the SCC may have changed and as
    // we're going to mutate this particular function we want to make sure the
    // proxy is in place to forward any invalidation events. We can use the
    // manager we get here for looking up results for functions other than this
    // node however because those functions aren't going to be mutated by this
    // pass.
    FunctionAnalysisManager &FAM =
        AM.getResult<FunctionAnalysisManagerCGSCCProxy>(*C, CG)
            .getManager();

    // Get the remarks emission analysis for the caller.
    auto &ORE = FAM.getResult<OptimizationRemarkEmitterAnalysis>(F);

    std::function<AssumptionCache &(Function &)> GetAssumptionCache =
        [&](Function &F) -> AssumptionCache & {
      return FAM.getResult<AssumptionAnalysis>(F);
    };
    auto GetBFI = [&](Function &F) -> BlockFrequencyInfo & {
      return FAM.getResult<BlockFrequencyAnalysis>(F);
    };

    auto GetInlineCost = [&](CallSite CS) {
      Function &Callee = *CS.getCalledFunction();
      auto &CalleeTTI = FAM.getResult<TargetIRAnalysis>(Callee);
      return getInlineCost(CS, Params, CalleeTTI, GetAssumptionCache, {GetBFI},
                           PSI, &ORE);
    };

    // Now process as many calls as we have within this caller in the sequnece.
    // We bail out as soon as the caller has to change so we can update the
    // call graph and prepare the context of that new caller.
    bool DidInline = false;
    for (; i < (int)Calls.size() && Calls[i].first.getCaller() == &F; ++i) {
      int InlineHistoryID;
      CallSite CS;
      std::tie(CS, InlineHistoryID) = Calls[i];
      Function &Callee = *CS.getCalledFunction();

      if (InlineHistoryID != -1 &&
          InlineHistoryIncludes(&Callee, InlineHistoryID, InlineHistory))
        continue;

      // Check if this inlining may repeat breaking an SCC apart that has
      // already been split once before. In that case, inlining here may
      // trigger infinite inlining, much like is prevented within the inliner
      // itself by the InlineHistory above, but spread across CGSCC iterations
      // and thus hidden from the full inline history.
      if (CG.lookupSCC(*CG.lookup(Callee)) == C &&
          UR.InlinedInternalEdges.count({&N, C})) {
        LLVM_DEBUG(dbgs() << "Skipping inlining internal SCC edge from a node "
                             "previously split out of this SCC by inlining: "
                          << F.getName() << " -> " << Callee.getName() << "\n");
        continue;
      }

      Optional<InlineCost> OIC = shouldInline(CS, GetInlineCost, ORE);
      // Check whether we want to inline this callsite.
      if (!OIC)
        continue;

      // Setup the data structure used to plumb customization into the
      // `InlineFunction` routine.
      InlineFunctionInfo IFI(
          /*cg=*/nullptr, &GetAssumptionCache, PSI,
          &FAM.getResult<BlockFrequencyAnalysis>(*(CS.getCaller())),
          &FAM.getResult<BlockFrequencyAnalysis>(Callee));

      // Get DebugLoc to report. CS will be invalid after Inliner.
      DebugLoc DLoc = CS->getDebugLoc();
      BasicBlock *Block = CS.getParent();

      using namespace ore;

      if (!InlineFunction(CS, IFI)) {
        ORE.emit([&]() {
          return OptimizationRemarkMissed(DEBUG_TYPE, "NotInlined", DLoc, Block)
                 << NV("Callee", &Callee) << " will not be inlined into "
                 << NV("Caller", &F);
        });
        continue;
      }
      DidInline = true;
      InlinedCallees.insert(&Callee);

      ORE.emit([&]() {
        bool AlwaysInline = OIC->isAlways();
        StringRef RemarkName = AlwaysInline ? "AlwaysInline" : "Inlined";
        OptimizationRemark R(DEBUG_TYPE, RemarkName, DLoc, Block);
        R << NV("Callee", &Callee) << " inlined into ";
        R << NV("Caller", &F);
        if (AlwaysInline)
          R << " with cost=always";
        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
    // below.
    for (Function *InlinedCallee : InlinedCallees) {
      LazyCallGraph::Node &CalleeN = *CG.lookup(*InlinedCallee);
      for (LazyCallGraph::Edge &E : *CalleeN)
        RC->insertTrivialRefEdge(N, E.getNode());
    }

    // At this point, since we have made changes we have at least removed
    // a call instruction. However, in the process we do some incremental
    // simplification of the surrounding code. This simplification can
    // essentially do all of the same things as a function pass and we can
    // re-use the exact same logic for updating the call graph to reflect the
    // change.
    LazyCallGraph::SCC *OldC = C;
    C = &updateCGAndAnalysisManagerForFunctionPass(CG, *C, N, AM, UR);
    LLVM_DEBUG(dbgs() << "Updated inlining SCC: " << *C << "\n");
    RC = &C->getOuterRefSCC();

    // If this causes an SCC to split apart into multiple smaller SCCs, there
    // is a subtle risk we need to prepare for. Other transformations may
    // expose an "infinite inlining" opportunity later, and because of the SCC
    // mutation, we will revisit this function and potentially re-inline. If we
    // do, and that re-inlining also has the potentially to mutate the SCC
    // structure, the infinite inlining problem can manifest through infinite
    // SCC splits and merges. To avoid this, we capture the originating caller
    // node and the SCC containing the call edge. This is a slight over
    // approximation of the possible inlining decisions that must be avoided,
    // but is relatively efficient to store.
    // FIXME: This seems like a very heavyweight way of retaining the inline
    // history, we should look for a more efficient way of tracking it.
    if (C != OldC && llvm::any_of(InlinedCallees, [&](Function *Callee) {
          return CG.lookupSCC(*CG.lookup(*Callee)) == OldC;
        })) {
      LLVM_DEBUG(dbgs() << "Inlined an internal call edge and split an SCC, "
                           "retaining this to avoid infinite inlining.\n");
      UR.InlinedInternalEdges.insert({&N, OldC});
    }
    InlinedCallees.clear();
  }

  // Now that we've finished inlining all of the calls across this SCC, delete
  // all of the trivially dead functions, updating the call graph and the CGSCC
  // pass manager in the process.
  //
  // Note that this walks a pointer set which has non-deterministic order but
  // that is OK as all we do is delete things and add pointers to unordered
  // sets.
  for (Function *DeadF : DeadFunctions) {
    // Get the necessary information out of the call graph and nuke the
    // function there. Also, cclear out any cached analyses.
    auto &DeadC = *CG.lookupSCC(*CG.lookup(*DeadF));
    FunctionAnalysisManager &FAM =
        AM.getResult<FunctionAnalysisManagerCGSCCProxy>(DeadC, CG)
            .getManager();
    FAM.clear(*DeadF, DeadF->getName());
    AM.clear(DeadC, DeadC.getName());
    auto &DeadRC = DeadC.getOuterRefSCC();
    CG.removeDeadFunction(*DeadF);

    // Mark the relevant parts of the call graph as invalid so we don't visit
    // them.
    UR.InvalidatedSCCs.insert(&DeadC);
    UR.InvalidatedRefSCCs.insert(&DeadRC);

    // And delete the actual function from the module.
    M.getFunctionList().erase(DeadF);
  }

  if (!Changed)
    return PreservedAnalyses::all();

  // Even if we change the IR, we update the core CGSCC data structures and so
  // can preserve the proxy to the function analysis manager.
  PreservedAnalyses PA;
  PA.preserve<FunctionAnalysisManagerCGSCCProxy>();
  return PA;
}
Exemplo n.º 6
0
PreservedAnalyses PostOrderFunctionAttrsPass::run(LazyCallGraph::SCC &C,
                                                  CGSCCAnalysisManager &AM) {
  Module &M = *C.begin()->getFunction().getParent();
  const ModuleAnalysisManager &MAM =
      AM.getResult<ModuleAnalysisManagerCGSCCProxy>(C).getManager();
  FunctionAnalysisManager &FAM =
      AM.getResult<FunctionAnalysisManagerCGSCCProxy>(C).getManager();

  // FIXME: Need some way to make it more reasonable to assume that this is
  // always cached.
  TargetLibraryInfo &TLI = *MAM.getCachedResult<TargetLibraryAnalysis>(M);

  // We pass a lambda into functions to wire them up to the analysis manager
  // for getting function analyses.
  auto AARGetter = [&](Function &F) -> AAResults & {
    return FAM.getResult<AAManager>(F);
  };

  // Fill SCCNodes with the elements of the SCC. Also track whether there are
  // any external or opt-none nodes that will prevent us from optimizing any
  // part of the SCC.
  SCCNodeSet SCCNodes;
  bool HasUnknownCall = false;
  for (LazyCallGraph::Node &N : C) {
    Function &F = N.getFunction();
    if (F.hasFnAttribute(Attribute::OptimizeNone)) {
      // Treat any function we're trying not to optimize as if it were an
      // indirect call and omit it from the node set used below.
      HasUnknownCall = true;
      continue;
    }
    // Track whether any functions in this SCC have an unknown call edge.
    // Note: if this is ever a performance hit, we can common it with
    // subsequent routines which also do scans over the instructions of the
    // function.
    if (!HasUnknownCall)
      for (Instruction &I : instructions(F))
        if (auto CS = CallSite(&I))
          if (!CS.getCalledFunction()) {
            HasUnknownCall = true;
            break;
          }

    SCCNodes.insert(&F);
  }

  bool Changed = false;
  Changed |= addReadAttrs(SCCNodes, AARGetter);
  Changed |= addArgumentAttrs(SCCNodes);

  // If we have no external nodes participating in the SCC, we can deduce some
  // more precise attributes as well.
  if (!HasUnknownCall) {
    Changed |= addNoAliasAttrs(SCCNodes);
    Changed |= addNonNullAttrs(SCCNodes, TLI);
    Changed |= removeConvergentAttrs(SCCNodes);
    Changed |= addNoRecurseAttrs(SCCNodes);
  }

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