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//===- CGSCCPassManager.cpp - Managing & running CGSCC passes -------------===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
#include "llvm/Analysis/CGSCCPassManager.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/Analysis/LazyCallGraph.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/PassManager.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <iterator>
#define DEBUG_TYPE "cgscc"
using namespace llvm;
// Explicit template instantiations and specialization definitions for core
// template typedefs.
namespace llvm {
// Explicit instantiations for the core proxy templates.
template class AllAnalysesOn<LazyCallGraph::SCC>;
template class AnalysisManager<LazyCallGraph::SCC, LazyCallGraph &>;
template class PassManager<LazyCallGraph::SCC, CGSCCAnalysisManager,
LazyCallGraph &, CGSCCUpdateResult &>;
template class InnerAnalysisManagerProxy<CGSCCAnalysisManager, Module>;
template class OuterAnalysisManagerProxy<ModuleAnalysisManager,
LazyCallGraph::SCC, LazyCallGraph &>;
template class OuterAnalysisManagerProxy<CGSCCAnalysisManager, Function>;
/// Explicitly specialize the pass manager run method to handle call graph
/// updates.
template <>
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: " << Pass->name() << " on " << *C << "\n";
PreservedAnalyses PassPA = Pass->run(*C, AM, G, UR);
// 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");
// 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.
// 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.
if (DebugLogging)
dbgs() << "Finished CGSCC pass manager run.\n";
return PA;
bool CGSCCAnalysisManagerModuleProxy::Result::invalidate(
Module &M, const PreservedAnalyses &PA,
ModuleAnalysisManager::Invalidator &Inv) {
// If literally everything is preserved, we're done.
if (PA.areAllPreserved())
return false; // This is still a valid proxy.
// If this proxy or the call graph is going to be invalidated, we also need
// to clear all the keys coming from that analysis.
// We also directly invalidate the FAM's module proxy if necessary, and if
// that proxy isn't preserved we can't preserve this proxy either. We rely on
// it to handle module -> function analysis invalidation in the face of
// structural changes and so if it's unavailable we conservatively clear the
// entire SCC layer as well rather than trying to do invalidation ourselves.
auto PAC = PA.getChecker<CGSCCAnalysisManagerModuleProxy>();
if (!(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Module>>()) ||
Inv.invalidate<LazyCallGraphAnalysis>(M, PA) ||
Inv.invalidate<FunctionAnalysisManagerModuleProxy>(M, PA)) {
// And the proxy itself should be marked as invalid so that we can observe
// the new call graph. This isn't strictly necessary because we cheat
// above, but is still useful.
return true;
// Directly check if the relevant set is preserved so we can short circuit
// invalidating SCCs below.
bool AreSCCAnalysesPreserved =
// Ok, we have a graph, so we can propagate the invalidation down into it.
for (auto &RC : G->postorder_ref_sccs())
for (auto &C : RC) {
Optional<PreservedAnalyses> InnerPA;
// Check to see whether the preserved set needs to be adjusted based on
// module-level analysis invalidation triggering deferred invalidation
// for this SCC.
if (auto *OuterProxy =
for (const auto &OuterInvalidationPair :
OuterProxy->getOuterInvalidations()) {
AnalysisKey *OuterAnalysisID = OuterInvalidationPair.first;
const auto &InnerAnalysisIDs = OuterInvalidationPair.second;
if (Inv.invalidate(OuterAnalysisID, M, PA)) {
if (!InnerPA)
InnerPA = PA;
for (AnalysisKey *InnerAnalysisID : InnerAnalysisIDs)
// Check if we needed a custom PA set. If so we'll need to run the inner
// invalidation.
if (InnerPA) {
InnerAM->invalidate(C, *InnerPA);
// Otherwise we only need to do invalidation if the original PA set didn't
// preserve all SCC analyses.
if (!AreSCCAnalysesPreserved)
InnerAM->invalidate(C, PA);
// Return false to indicate that this result is still a valid proxy.
return false;
template <>
CGSCCAnalysisManagerModuleProxy::run(Module &M, ModuleAnalysisManager &AM) {
// Force the Function analysis manager to also be available so that it can
// be accessed in an SCC analysis and proxied onward to function passes.
// FIXME: It is pretty awkward to just drop the result here and assert that
// we can find it again later.
return Result(*InnerAM, AM.getResult<LazyCallGraphAnalysis>(M));
AnalysisKey FunctionAnalysisManagerCGSCCProxy::Key;
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 "
// 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());
bool FunctionAnalysisManagerCGSCCProxy::Result::invalidate(
LazyCallGraph::SCC &C, const PreservedAnalyses &PA,
CGSCCAnalysisManager::Invalidator &Inv) {
// If literally everything is preserved, we're done.
if (PA.areAllPreserved())
return false; // This is still a valid proxy.
// If this proxy isn't marked as preserved, then even if the result remains
// valid, the key itself may no longer be valid, so we clear everything.
// Note that in order to preserve this proxy, a module pass must ensure that
// the FAM has been completely updated to handle the deletion of functions.
// Specifically, any FAM-cached results for those functions need to have been
// forcibly cleared. When preserved, this proxy will only invalidate results
// cached on functions *still in the module* at the end of the module pass.
auto PAC = PA.getChecker<FunctionAnalysisManagerCGSCCProxy>();
if (!PAC.preserved() && !PAC.preservedSet<AllAnalysesOn<LazyCallGraph::SCC>>()) {
for (LazyCallGraph::Node &N : C)
FAM->clear(N.getFunction(), N.getFunction().getName());
return true;
// Directly check if the relevant set is preserved.
bool AreFunctionAnalysesPreserved =
// Now walk all the functions to see if any inner analysis invalidation is
// necessary.
for (LazyCallGraph::Node &N : C) {
Function &F = N.getFunction();
Optional<PreservedAnalyses> FunctionPA;
// Check to see whether the preserved set needs to be pruned based on
// SCC-level analysis invalidation that triggers deferred invalidation
// registered with the outer analysis manager proxy for this function.
if (auto *OuterProxy =
for (const auto &OuterInvalidationPair :
OuterProxy->getOuterInvalidations()) {
AnalysisKey *OuterAnalysisID = OuterInvalidationPair.first;
const auto &InnerAnalysisIDs = OuterInvalidationPair.second;
if (Inv.invalidate(OuterAnalysisID, C, PA)) {
if (!FunctionPA)
FunctionPA = PA;
for (AnalysisKey *InnerAnalysisID : InnerAnalysisIDs)
// Check if we needed a custom PA set, and if so we'll need to run the
// inner invalidation.
if (FunctionPA) {
FAM->invalidate(F, *FunctionPA);
// Otherwise we only need to do invalidation if the original PA set didn't
// preserve all function analyses.
if (!AreFunctionAnalysesPreserved)
FAM->invalidate(F, PA);
// Return false to indicate that this result is still a valid proxy.
return false;
} // end namespace llvm
/// When a new SCC is created for the graph and there might be function
/// analysis results cached for the functions now in that SCC two forms of
/// updates are required.
/// First, a proxy from the SCC to the FunctionAnalysisManager needs to be
/// created so that any subsequent invalidation events to the SCC are
/// propagated to the function analysis results cached for functions within it.
/// Second, if any of the functions within the SCC have analysis results with
/// outer analysis dependencies, then those dependencies would point to the
/// *wrong* SCC's analysis result. We forcibly invalidate the necessary
/// function analyses so that they don't retain stale handles.
static void updateNewSCCFunctionAnalyses(LazyCallGraph::SCC &C,
LazyCallGraph &G,
CGSCCAnalysisManager &AM) {
// Get the relevant function analysis manager.
auto &FAM =
AM.getResult<FunctionAnalysisManagerCGSCCProxy>(C, G).getManager();
// Now walk the functions in this SCC and invalidate any function analysis
// results that might have outer dependencies on an SCC analysis.
for (LazyCallGraph::Node &N : C) {
Function &F = N.getFunction();
auto *OuterProxy =
if (!OuterProxy)
// No outer analyses were queried, nothing to do.
// Forcibly abandon all the inner analyses with dependencies, but
// invalidate nothing else.
auto PA = PreservedAnalyses::all();
for (const auto &OuterInvalidationPair :
OuterProxy->getOuterInvalidations()) {
const auto &InnerAnalysisIDs = OuterInvalidationPair.second;
for (AnalysisKey *InnerAnalysisID : InnerAnalysisIDs)
// Now invalidate anything we found.
FAM.invalidate(F, PA);
/// Helper function to update both the \c CGSCCAnalysisManager \p AM and the \c
/// CGSCCPassManager's \c CGSCCUpdateResult \p UR based on a range of newly
/// added SCCs.
/// The range of new SCCs must be in postorder already. The SCC they were split
/// out of must be provided as \p C. The current node being mutated and
/// triggering updates must be passed as \p N.
/// This function returns the SCC containing \p N. This will be either \p C if
/// no new SCCs have been split out, or it will be the new SCC containing \p N.
template <typename SCCRangeT>
static LazyCallGraph::SCC *
incorporateNewSCCRange(const SCCRangeT &NewSCCRange, LazyCallGraph &G,
LazyCallGraph::Node &N, LazyCallGraph::SCC *C,
CGSCCAnalysisManager &AM, CGSCCUpdateResult &UR) {
using SCC = LazyCallGraph::SCC;
if (NewSCCRange.begin() == NewSCCRange.end())
return C;
// Add the current SCC to the worklist as its shape has changed.
LLVM_DEBUG(dbgs() << "Enqueuing the existing SCC in the worklist:" << *C
<< "\n");
SCC *OldC = C;
// Update the current SCC. Note that if we have new SCCs, this must actually
// change the SCC.
assert(C != &*NewSCCRange.begin() &&
"Cannot insert new SCCs without changing current SCC!");
C = &*NewSCCRange.begin();
assert(G.lookupSCC(N) == C && "Failed to update current SCC!");
// If we had a cached FAM proxy originally, we will want to create more of
// them for each SCC that was split off.
bool NeedFAMProxy =
AM.getCachedResult<FunctionAnalysisManagerCGSCCProxy>(*OldC) != nullptr;
// We need to propagate an invalidation call to all but the newly current SCC
// because the outer pass manager won't do that for us after splitting them.
// FIXME: We should accept a PreservedAnalysis from the CG updater so that if
// there are preserved analysis we can avoid invalidating them here for
// split-off SCCs.
// We know however that this will preserve any FAM proxy so go ahead and mark
// that.
PreservedAnalyses PA;
AM.invalidate(*OldC, PA);
// Ensure the now-current SCC's function analyses are updated.
if (NeedFAMProxy)
updateNewSCCFunctionAnalyses(*C, G, AM);
for (SCC &NewC : llvm::reverse(make_range(std::next(NewSCCRange.begin()),
NewSCCRange.end()))) {
assert(C != &NewC && "No need to re-visit the current SCC!");
assert(OldC != &NewC && "Already handled the original SCC!");
LLVM_DEBUG(dbgs() << "Enqueuing a newly formed SCC:" << NewC << "\n");
// Ensure new SCCs' function analyses are updated.
if (NeedFAMProxy)
updateNewSCCFunctionAnalyses(NewC, G, AM);
// Also propagate a normal invalidation to the new SCC as only the current
// will get one from the pass manager infrastructure.
AM.invalidate(NewC, PA);
return C;
LazyCallGraph::SCC &llvm::updateCGAndAnalysisManagerForFunctionPass(
LazyCallGraph &G, LazyCallGraph::SCC &InitialC, LazyCallGraph::Node &N,
CGSCCAnalysisManager &AM, CGSCCUpdateResult &UR) {
using Node = LazyCallGraph::Node;
using Edge = LazyCallGraph::Edge;
using SCC = LazyCallGraph::SCC;
using RefSCC = LazyCallGraph::RefSCC;
RefSCC &InitialRC = InitialC.getOuterRefSCC();
SCC *C = &InitialC;
RefSCC *RC = &InitialRC;
Function &F = N.getFunction();
// Walk the function body and build up the set of retained, promoted, and
// demoted edges.
SmallVector<Constant *, 16> Worklist;
SmallPtrSet<Constant *, 16> Visited;
SmallPtrSet<Node *, 16> RetainedEdges;
SmallSetVector<Node *, 4> PromotedRefTargets;
SmallSetVector<Node *, 4> DemotedCallTargets;
// First walk the function and handle all called functions. We do this first
// because if there is a single call edge, whether there are ref edges is
// irrelevant.
for (Instruction &I : instructions(F))
if (auto CS = CallSite(&I))
if (Function *Callee = CS.getCalledFunction())
if (Visited.insert(Callee).second && !Callee->isDeclaration()) {
Node &CalleeN = *G.lookup(*Callee);
Edge *E = N->lookup(CalleeN);
// FIXME: We should really handle adding new calls. While it will
// make downstream usage more complex, there is no fundamental
// limitation and it will allow passes within the CGSCC to be a bit
// more flexible in what transforms they can do. Until then, we
// verify that new calls haven't been introduced.
assert(E && "No function transformations should introduce *new* "
"call edges! Any new calls should be modeled as "
"promoted existing ref edges!");
bool Inserted = RetainedEdges.insert(&CalleeN).second;
assert(Inserted && "We should never visit a function twice.");
if (!E->isCall())
// Now walk all references.
for (Instruction &I : instructions(F))
for (Value *Op : I.operand_values())
if (auto *C = dyn_cast<Constant>(Op))
if (Visited.insert(C).second)
auto VisitRef = [&](Function &Referee) {
Node &RefereeN = *G.lookup(Referee);
Edge *E = N->lookup(RefereeN);
// FIXME: Similarly to new calls, we also currently preclude
// introducing new references. See above for details.
assert(E && "No function transformations should introduce *new* ref "
"edges! Any new ref edges would require IPO which "
"function passes aren't allowed to do!");
bool Inserted = RetainedEdges.insert(&RefereeN).second;
assert(Inserted && "We should never visit a function twice.");
if (E->isCall())
LazyCallGraph::visitReferences(Worklist, Visited, VisitRef);
// 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))
// 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()))
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.
// Remove the easy cases quickly and actually pull them out of our list.
[&](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;
// 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.
// 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!");
// The RC worklist is in reverse postorder, so we enqueue the new ones in
// RPO except for the one which contains the source node as that is the
// "bottom" we will continue processing in the bottom-up walk.
assert(NewRefSCCs.front() == RC &&
"New current RefSCC not first in the returned list!");
for (RefSCC *NewRC : llvm::reverse(make_range(std::next(NewRefSCCs.begin()),
NewRefSCCs.end()))) {
assert(NewRC != RC && "Should not encounter the current RefSCC further "
"in the postorder list of new RefSCCs.");
LLVM_DEBUG(dbgs() << "Enqueuing a new RefSCC in the update worklist: "
<< *NewRC << "\n");
// Next demote all the call edges that are now ref edges. This helps make
// the SCCs small which should minimize the work below as we don't want to
// form cycles that this would break.
for (Node *RefTarget : DemotedCallTargets) {
SCC &TargetC = *G.lookupSCC(*RefTarget);
RefSCC &TargetRC = TargetC.getOuterRefSCC();
// The easy case is when the target RefSCC is not this RefSCC. This is
// only supported when the target RefSCC is a child of this RefSCC.
if (&TargetRC != RC) {
assert(RC->isAncestorOf(TargetRC) &&
"Cannot potentially form RefSCC cycles here!");
RC->switchOutgoingEdgeToRef(N, *RefTarget);
LLVM_DEBUG(dbgs() << "Switch outgoing call edge to a ref edge from '" << N
<< "' to '" << *RefTarget << "'\n");
// We are switching an internal call edge to a ref edge. This may split up
// some SCCs.
if (C != &TargetC) {
// For separate SCCs this is trivial.
RC->switchTrivialInternalEdgeToRef(N, *RefTarget);
// Now update the call graph.
C = incorporateNewSCCRange(RC->switchInternalEdgeToRef(N, *RefTarget), G, N,
C, AM, UR);
// Now promote ref edges into call edges.
for (Node *CallTarget : PromotedRefTargets) {
SCC &TargetC = *G.lookupSCC(*CallTarget);
RefSCC &TargetRC = TargetC.getOuterRefSCC();
// The easy case is when the target RefSCC is not this RefSCC. This is
// only supported when the target RefSCC is a child of this RefSCC.
if (&TargetRC != RC) {
assert(RC->isAncestorOf(TargetRC) &&
"Cannot potentially form RefSCC cycles here!");
RC->switchOutgoingEdgeToCall(N, *CallTarget);
LLVM_DEBUG(dbgs() << "Switch outgoing ref edge to a call edge from '" << N
<< "' to '" << *CallTarget << "'\n");
LLVM_DEBUG(dbgs() << "Switch an internal ref edge to a call edge from '"
<< N << "' to '" << *CallTarget << "'\n");
// Otherwise we are switching an internal ref edge to a call edge. This
// may merge away some SCCs, and we add those to the UpdateResult. We also
// need to make sure to update the worklist in the event SCCs have moved
// before the current one in the post-order sequence
bool HasFunctionAnalysisProxy = false;
auto InitialSCCIndex = RC->find(*C) - RC->begin();
bool FormedCycle = RC->switchInternalEdgeToCall(
N, *CallTarget, [&](ArrayRef<SCC *> MergedSCCs) {
for (SCC *MergedC : MergedSCCs) {
assert(MergedC != &TargetC && "Cannot merge away the target SCC!");
HasFunctionAnalysisProxy |=
*MergedC) != nullptr;
// Mark that this SCC will no longer be valid.
// FIXME: We should really do a 'clear' here to forcibly release
// memory, but we don't have a good way of doing that and
// preserving the function analyses.
auto PA = PreservedAnalyses::allInSet<AllAnalysesOn<Function>>();
AM.invalidate(*MergedC, PA);
// If we formed a cycle by creating this call, we need to update more data
// structures.
if (FormedCycle) {
C = &TargetC;
assert(G.lookupSCC(N) == C && "Failed to update current SCC!");
// If one of the invalidated SCCs had a cached proxy to a function
// analysis manager, we need to create a proxy in the new current SCC as
// the invalidated SCCs had their functions moved.
if (HasFunctionAnalysisProxy)
AM.getResult<FunctionAnalysisManagerCGSCCProxy>(*C, G);
// Any analyses cached for this SCC are no longer precise as the shape
// has changed by introducing this cycle. However, we have taken care to
// update the proxies so it remains valide.
auto PA = PreservedAnalyses::allInSet<AllAnalysesOn<Function>>();
AM.invalidate(*C, PA);
auto NewSCCIndex = RC->find(*C) - RC->begin();
// If we have actually moved an SCC to be topologically "below" the current
// one due to merging, we will need to revisit the current SCC after
// visiting those moved SCCs.
// It is critical that we *do not* revisit the current SCC unless we
// actually move SCCs in the process of merging because otherwise we may
// form a cycle where an SCC is split apart, merged, split, merged and so
// on infinitely.
if (InitialSCCIndex < NewSCCIndex) {
// Put our current SCC back onto the worklist as we'll visit other SCCs
// that are now definitively ordered prior to the current one in the
// post-order sequence, and may end up observing more precise context to
// optimize the current SCC.
LLVM_DEBUG(dbgs() << "Enqueuing the existing SCC in the worklist: " << *C
<< "\n");
// Enqueue in reverse order as we pop off the back of the worklist.
for (SCC &MovedC : llvm::reverse(make_range(RC->begin() + InitialSCCIndex,
RC->begin() + NewSCCIndex))) {
LLVM_DEBUG(dbgs() << "Enqueuing a newly earlier in post-order SCC: "
<< MovedC << "\n");
assert(!UR.InvalidatedSCCs.count(C) && "Invalidated the current SCC!");
assert(!UR.InvalidatedRefSCCs.count(RC) && "Invalidated the current RefSCC!");
assert(&C->getOuterRefSCC() == RC && "Current SCC not in current RefSCC!");
// Record the current RefSCC and SCC for higher layers of the CGSCC pass
// manager now that all the updates have been applied.
if (RC != &InitialRC)
UR.UpdatedRC = RC;
if (C != &InitialC)
UR.UpdatedC = C;
return *C;