LCOV - code coverage report
Current view: top level - lib/Analysis - LazyCallGraph.cpp (source / functions) Hit Total Coverage
Test: llvm-toolchain.info Lines: 493 523 94.3 %
Date: 2018-07-13 00:08:38 Functions: 56 60 93.3 %
Legend: Lines: hit not hit

          Line data    Source code
       1             : //===- LazyCallGraph.cpp - Analysis of a Module's call graph --------------===//
       2             : //
       3             : //                     The LLVM Compiler Infrastructure
       4             : //
       5             : // This file is distributed under the University of Illinois Open Source
       6             : // License. See LICENSE.TXT for details.
       7             : //
       8             : //===----------------------------------------------------------------------===//
       9             : 
      10             : #include "llvm/Analysis/LazyCallGraph.h"
      11             : #include "llvm/ADT/ArrayRef.h"
      12             : #include "llvm/ADT/STLExtras.h"
      13             : #include "llvm/ADT/ScopeExit.h"
      14             : #include "llvm/ADT/Sequence.h"
      15             : #include "llvm/ADT/SmallPtrSet.h"
      16             : #include "llvm/ADT/SmallVector.h"
      17             : #include "llvm/ADT/iterator_range.h"
      18             : #include "llvm/Analysis/TargetLibraryInfo.h"
      19             : #include "llvm/Config/llvm-config.h"
      20             : #include "llvm/IR/CallSite.h"
      21             : #include "llvm/IR/Function.h"
      22             : #include "llvm/IR/GlobalVariable.h"
      23             : #include "llvm/IR/Instruction.h"
      24             : #include "llvm/IR/Module.h"
      25             : #include "llvm/IR/PassManager.h"
      26             : #include "llvm/Support/Casting.h"
      27             : #include "llvm/Support/Compiler.h"
      28             : #include "llvm/Support/Debug.h"
      29             : #include "llvm/Support/GraphWriter.h"
      30             : #include "llvm/Support/raw_ostream.h"
      31             : #include <algorithm>
      32             : #include <cassert>
      33             : #include <cstddef>
      34             : #include <iterator>
      35             : #include <string>
      36             : #include <tuple>
      37             : #include <utility>
      38             : 
      39             : using namespace llvm;
      40             : 
      41             : #define DEBUG_TYPE "lcg"
      42             : 
      43          14 : void LazyCallGraph::EdgeSequence::insertEdgeInternal(Node &TargetN,
      44             :                                                      Edge::Kind EK) {
      45          28 :   EdgeIndexMap.insert({&TargetN, Edges.size()});
      46          14 :   Edges.emplace_back(TargetN, EK);
      47          14 : }
      48             : 
      49         134 : void LazyCallGraph::EdgeSequence::setEdgeKind(Node &TargetN, Edge::Kind EK) {
      50         268 :   Edges[EdgeIndexMap.find(&TargetN)->second].setKind(EK);
      51         134 : }
      52             : 
      53         426 : bool LazyCallGraph::EdgeSequence::removeEdgeInternal(Node &TargetN) {
      54         426 :   auto IndexMapI = EdgeIndexMap.find(&TargetN);
      55         426 :   if (IndexMapI == EdgeIndexMap.end())
      56             :     return false;
      57             : 
      58         682 :   Edges[IndexMapI->second] = Edge();
      59             :   EdgeIndexMap.erase(IndexMapI);
      60         341 :   return true;
      61             : }
      62             : 
      63        2016 : static void addEdge(SmallVectorImpl<LazyCallGraph::Edge> &Edges,
      64             :                     DenseMap<LazyCallGraph::Node *, int> &EdgeIndexMap,
      65             :                     LazyCallGraph::Node &N, LazyCallGraph::Edge::Kind EK) {
      66        2016 :   if (!EdgeIndexMap.insert({&N, Edges.size()}).second)
      67             :     return;
      68             : 
      69             :   LLVM_DEBUG(dbgs() << "    Added callable function: " << N.getName() << "\n");
      70        2001 :   Edges.emplace_back(LazyCallGraph::Edge(N, EK));
      71             : }
      72             : 
      73        1188 : LazyCallGraph::EdgeSequence &LazyCallGraph::Node::populateSlow() {
      74             :   assert(!Edges && "Must not have already populated the edges for this node!");
      75             : 
      76             :   LLVM_DEBUG(dbgs() << "  Adding functions called by '" << getName()
      77             :                     << "' to the graph.\n");
      78             : 
      79        2376 :   Edges = EdgeSequence();
      80             : 
      81             :   SmallVector<Constant *, 16> Worklist;
      82             :   SmallPtrSet<Function *, 4> Callees;
      83             :   SmallPtrSet<Constant *, 16> Visited;
      84             : 
      85             :   // Find all the potential call graph edges in this function. We track both
      86             :   // actual call edges and indirect references to functions. The direct calls
      87             :   // are trivially added, but to accumulate the latter we walk the instructions
      88             :   // and add every operand which is a constant to the worklist to process
      89             :   // afterward.
      90             :   //
      91             :   // Note that we consider *any* function with a definition to be a viable
      92             :   // edge. Even if the function's definition is subject to replacement by
      93             :   // some other module (say, a weak definition) there may still be
      94             :   // optimizations which essentially speculate based on the definition and
      95             :   // a way to check that the specific definition is in fact the one being
      96             :   // used. For example, this could be done by moving the weak definition to
      97             :   // a strong (internal) definition and making the weak definition be an
      98             :   // alias. Then a test of the address of the weak function against the new
      99             :   // strong definition's address would be an effective way to determine the
     100             :   // safety of optimizing a direct call edge.
     101        4235 :   for (BasicBlock &BB : *F)
     102        8747 :     for (Instruction &I : BB) {
     103        6888 :       if (auto CS = CallSite(&I))
     104             :         if (Function *Callee = CS.getCalledFunction())
     105        3340 :           if (!Callee->isDeclaration())
     106         834 :             if (Callees.insert(Callee).second) {
     107         793 :               Visited.insert(Callee);
     108         793 :               addEdge(Edges->Edges, Edges->EdgeIndexMap, G->get(*Callee),
     109             :                       LazyCallGraph::Edge::Call);
     110             :             }
     111             : 
     112       22841 :       for (Value *Op : I.operand_values())
     113        9065 :         if (Constant *C = dyn_cast<Constant>(Op))
     114        5005 :           if (Visited.insert(C).second)
     115        1581 :             Worklist.push_back(C);
     116             :     }
     117             : 
     118             :   // We've collected all the constant (and thus potentially function or
     119             :   // function containing) operands to all of the instructions in the function.
     120             :   // Process them (recursively) collecting every function found.
     121        1340 :   visitReferences(Worklist, Visited, [&](Function &F) {
     122         152 :     addEdge(Edges->Edges, Edges->EdgeIndexMap, G->get(F),
     123             :             LazyCallGraph::Edge::Ref);
     124         152 :   });
     125             : 
     126             :   // Add implicit reference edges to any defined libcall functions (if we
     127             :   // haven't found an explicit edge).
     128        2412 :   for (auto *F : G->LibFunctions)
     129          18 :     if (!Visited.count(F))
     130          16 :       addEdge(Edges->Edges, Edges->EdgeIndexMap, G->get(*F),
     131             :               LazyCallGraph::Edge::Ref);
     132             : 
     133        1188 :   return *Edges;
     134             : }
     135             : 
     136          20 : void LazyCallGraph::Node::replaceFunction(Function &NewF) {
     137             :   assert(F != &NewF && "Must not replace a function with itself!");
     138          20 :   F = &NewF;
     139          20 : }
     140             : 
     141             : #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
     142             : LLVM_DUMP_METHOD void LazyCallGraph::Node::dump() const {
     143             :   dbgs() << *this << '\n';
     144             : }
     145             : #endif
     146             : 
     147        1185 : static bool isKnownLibFunction(Function &F, TargetLibraryInfo &TLI) {
     148             :   LibFunc LF;
     149             : 
     150             :   // Either this is a normal library function or a "vectorizable" function.
     151        2367 :   return TLI.getLibFunc(F, LF) || TLI.isFunctionVectorizable(F.getName());
     152             : }
     153             : 
     154         879 : LazyCallGraph::LazyCallGraph(Module &M, TargetLibraryInfo &TLI) {
     155             :   LLVM_DEBUG(dbgs() << "Building CG for module: " << M.getModuleIdentifier()
     156             :                     << "\n");
     157        1799 :   for (Function &F : M) {
     158        1506 :     if (F.isDeclaration())
     159         321 :       continue;
     160             :     // If this function is a known lib function to LLVM then we want to
     161             :     // synthesize reference edges to it to model the fact that LLVM can turn
     162             :     // arbitrary code into a library function call.
     163        1185 :     if (isKnownLibFunction(F, TLI))
     164           3 :       LibFunctions.insert(&F);
     165             : 
     166         141 :     if (F.hasLocalLinkage())
     167         141 :       continue;
     168             : 
     169             :     // External linkage defined functions have edges to them from other
     170             :     // modules.
     171             :     LLVM_DEBUG(dbgs() << "  Adding '" << F.getName()
     172             :                       << "' to entry set of the graph.\n");
     173        1044 :     addEdge(EntryEdges.Edges, EntryEdges.EdgeIndexMap, get(F), Edge::Ref);
     174             :   }
     175             : 
     176             :   // Now add entry nodes for functions reachable via initializers to globals.
     177             :   SmallVector<Constant *, 16> Worklist;
     178             :   SmallPtrSet<Constant *, 16> Visited;
     179         391 :   for (GlobalVariable &GV : M.globals())
     180          98 :     if (GV.hasInitializer())
     181          82 :       if (Visited.insert(GV.getInitializer()).second)
     182          74 :         Worklist.push_back(GV.getInitializer());
     183             : 
     184             :   LLVM_DEBUG(
     185             :       dbgs() << "  Adding functions referenced by global initializers to the "
     186             :                 "entry set.\n");
     187         304 :   visitReferences(Worklist, Visited, [&](Function &F) {
     188          11 :     addEdge(EntryEdges.Edges, EntryEdges.EdgeIndexMap, get(F),
     189             :             LazyCallGraph::Edge::Ref);
     190          11 :   });
     191         293 : }
     192             : 
     193         544 : LazyCallGraph::LazyCallGraph(LazyCallGraph &&G)
     194             :     : BPA(std::move(G.BPA)), NodeMap(std::move(G.NodeMap)),
     195         544 :       EntryEdges(std::move(G.EntryEdges)), SCCBPA(std::move(G.SCCBPA)),
     196             :       SCCMap(std::move(G.SCCMap)),
     197        1088 :       LibFunctions(std::move(G.LibFunctions)) {
     198         544 :   updateGraphPtrs();
     199         544 : }
     200             : 
     201           0 : LazyCallGraph &LazyCallGraph::operator=(LazyCallGraph &&G) {
     202             :   BPA = std::move(G.BPA);
     203           0 :   NodeMap = std::move(G.NodeMap);
     204             :   EntryEdges = std::move(G.EntryEdges);
     205             :   SCCBPA = std::move(G.SCCBPA);
     206           0 :   SCCMap = std::move(G.SCCMap);
     207             :   LibFunctions = std::move(G.LibFunctions);
     208           0 :   updateGraphPtrs();
     209           0 :   return *this;
     210             : }
     211             : 
     212             : #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
     213             : LLVM_DUMP_METHOD void LazyCallGraph::SCC::dump() const {
     214             :   dbgs() << *this << '\n';
     215             : }
     216             : #endif
     217             : 
     218             : #ifndef NDEBUG
     219             : void LazyCallGraph::SCC::verify() {
     220             :   assert(OuterRefSCC && "Can't have a null RefSCC!");
     221             :   assert(!Nodes.empty() && "Can't have an empty SCC!");
     222             : 
     223             :   for (Node *N : Nodes) {
     224             :     assert(N && "Can't have a null node!");
     225             :     assert(OuterRefSCC->G->lookupSCC(*N) == this &&
     226             :            "Node does not map to this SCC!");
     227             :     assert(N->DFSNumber == -1 &&
     228             :            "Must set DFS numbers to -1 when adding a node to an SCC!");
     229             :     assert(N->LowLink == -1 &&
     230             :            "Must set low link to -1 when adding a node to an SCC!");
     231             :     for (Edge &E : **N)
     232             :       assert(E.getNode().isPopulated() && "Can't have an unpopulated node!");
     233             :   }
     234             : }
     235             : #endif
     236             : 
     237          14 : bool LazyCallGraph::SCC::isParentOf(const SCC &C) const {
     238          14 :   if (this == &C)
     239             :     return false;
     240             : 
     241          20 :   for (Node &N : *this)
     242          70 :     for (Edge &E : N->calls())
     243          58 :       if (OuterRefSCC->G->lookupSCC(E.getNode()) == &C)
     244           8 :         return true;
     245             : 
     246             :   // No edges found.
     247             :   return false;
     248             : }
     249             : 
     250          10 : bool LazyCallGraph::SCC::isAncestorOf(const SCC &TargetC) const {
     251          10 :   if (this == &TargetC)
     252             :     return false;
     253             : 
     254          10 :   LazyCallGraph &G = *OuterRefSCC->G;
     255             : 
     256             :   // Start with this SCC.
     257          10 :   SmallPtrSet<const SCC *, 16> Visited = {this};
     258          20 :   SmallVector<const SCC *, 16> Worklist = {this};
     259             : 
     260             :   // Walk down the graph until we run out of edges or find a path to TargetC.
     261             :   do {
     262             :     const SCC &C = *Worklist.pop_back_val();
     263          22 :     for (Node &N : C)
     264          72 :       for (Edge &E : N->calls()) {
     265             :         SCC *CalleeC = G.lookupSCC(E.getNode());
     266          30 :         if (!CalleeC)
     267           0 :           continue;
     268             : 
     269             :         // If the callee's SCC is the TargetC, we're done.
     270          30 :         if (CalleeC == &TargetC)
     271          10 :           return true;
     272             : 
     273             :         // If this is the first time we've reached this SCC, put it on the
     274             :         // worklist to recurse through.
     275          20 :         if (Visited.insert(CalleeC).second)
     276          20 :           Worklist.push_back(CalleeC);
     277             :       }
     278           6 :   } while (!Worklist.empty());
     279             : 
     280             :   // No paths found.
     281             :   return false;
     282             : }
     283             : 
     284        2066 : LazyCallGraph::RefSCC::RefSCC(LazyCallGraph &G) : G(&G) {}
     285             : 
     286             : #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
     287             : LLVM_DUMP_METHOD void LazyCallGraph::RefSCC::dump() const {
     288             :   dbgs() << *this << '\n';
     289             : }
     290             : #endif
     291             : 
     292             : #ifndef NDEBUG
     293             : void LazyCallGraph::RefSCC::verify() {
     294             :   assert(G && "Can't have a null graph!");
     295             :   assert(!SCCs.empty() && "Can't have an empty SCC!");
     296             : 
     297             :   // Verify basic properties of the SCCs.
     298             :   SmallPtrSet<SCC *, 4> SCCSet;
     299             :   for (SCC *C : SCCs) {
     300             :     assert(C && "Can't have a null SCC!");
     301             :     C->verify();
     302             :     assert(&C->getOuterRefSCC() == this &&
     303             :            "SCC doesn't think it is inside this RefSCC!");
     304             :     bool Inserted = SCCSet.insert(C).second;
     305             :     assert(Inserted && "Found a duplicate SCC!");
     306             :     auto IndexIt = SCCIndices.find(C);
     307             :     assert(IndexIt != SCCIndices.end() &&
     308             :            "Found an SCC that doesn't have an index!");
     309             :   }
     310             : 
     311             :   // Check that our indices map correctly.
     312             :   for (auto &SCCIndexPair : SCCIndices) {
     313             :     SCC *C = SCCIndexPair.first;
     314             :     int i = SCCIndexPair.second;
     315             :     assert(C && "Can't have a null SCC in the indices!");
     316             :     assert(SCCSet.count(C) && "Found an index for an SCC not in the RefSCC!");
     317             :     assert(SCCs[i] == C && "Index doesn't point to SCC!");
     318             :   }
     319             : 
     320             :   // Check that the SCCs are in fact in post-order.
     321             :   for (int i = 0, Size = SCCs.size(); i < Size; ++i) {
     322             :     SCC &SourceSCC = *SCCs[i];
     323             :     for (Node &N : SourceSCC)
     324             :       for (Edge &E : *N) {
     325             :         if (!E.isCall())
     326             :           continue;
     327             :         SCC &TargetSCC = *G->lookupSCC(E.getNode());
     328             :         if (&TargetSCC.getOuterRefSCC() == this) {
     329             :           assert(SCCIndices.find(&TargetSCC)->second <= i &&
     330             :                  "Edge between SCCs violates post-order relationship.");
     331             :           continue;
     332             :         }
     333             :       }
     334             :   }
     335             : }
     336             : #endif
     337             : 
     338          36 : bool LazyCallGraph::RefSCC::isParentOf(const RefSCC &RC) const {
     339          36 :   if (&RC == this)
     340             :     return false;
     341             : 
     342             :   // Search all edges to see if this is a parent.
     343          45 :   for (SCC &C : *this)
     344          66 :     for (Node &N : C)
     345         118 :       for (Edge &E : *N)
     346         176 :         if (G->lookupRefSCC(E.getNode()) == &RC)
     347             :           return true;
     348             : 
     349             :   return false;
     350             : }
     351             : 
     352          21 : bool LazyCallGraph::RefSCC::isAncestorOf(const RefSCC &RC) const {
     353          21 :   if (&RC == this)
     354             :     return false;
     355             : 
     356             :   // For each descendant of this RefSCC, see if one of its children is the
     357             :   // argument. If not, add that descendant to the worklist and continue
     358             :   // searching.
     359             :   SmallVector<const RefSCC *, 4> Worklist;
     360             :   SmallPtrSet<const RefSCC *, 4> Visited;
     361          19 :   Worklist.push_back(this);
     362          19 :   Visited.insert(this);
     363             :   do {
     364             :     const RefSCC &DescendantRC = *Worklist.pop_back_val();
     365          37 :     for (SCC &C : DescendantRC)
     366          56 :       for (Node &N : C)
     367         101 :         for (Edge &E : *N) {
     368         142 :           auto *ChildRC = G->lookupRefSCC(E.getNode());
     369          71 :           if (ChildRC == &RC)
     370             :             return true;
     371          81 :           if (!ChildRC || !Visited.insert(ChildRC).second)
     372          31 :             continue;
     373          25 :           Worklist.push_back(ChildRC);
     374             :         }
     375          11 :   } while (!Worklist.empty());
     376             : 
     377             :   return false;
     378             : }
     379             : 
     380             : /// Generic helper that updates a postorder sequence of SCCs for a potentially
     381             : /// cycle-introducing edge insertion.
     382             : ///
     383             : /// A postorder sequence of SCCs of a directed graph has one fundamental
     384             : /// property: all deges in the DAG of SCCs point "up" the sequence. That is,
     385             : /// all edges in the SCC DAG point to prior SCCs in the sequence.
     386             : ///
     387             : /// This routine both updates a postorder sequence and uses that sequence to
     388             : /// compute the set of SCCs connected into a cycle. It should only be called to
     389             : /// insert a "downward" edge which will require changing the sequence to
     390             : /// restore it to a postorder.
     391             : ///
     392             : /// When inserting an edge from an earlier SCC to a later SCC in some postorder
     393             : /// sequence, all of the SCCs which may be impacted are in the closed range of
     394             : /// those two within the postorder sequence. The algorithm used here to restore
     395             : /// the state is as follows:
     396             : ///
     397             : /// 1) Starting from the source SCC, construct a set of SCCs which reach the
     398             : ///    source SCC consisting of just the source SCC. Then scan toward the
     399             : ///    target SCC in postorder and for each SCC, if it has an edge to an SCC
     400             : ///    in the set, add it to the set. Otherwise, the source SCC is not
     401             : ///    a successor, move it in the postorder sequence to immediately before
     402             : ///    the source SCC, shifting the source SCC and all SCCs in the set one
     403             : ///    position toward the target SCC. Stop scanning after processing the
     404             : ///    target SCC.
     405             : /// 2) If the source SCC is now past the target SCC in the postorder sequence,
     406             : ///    and thus the new edge will flow toward the start, we are done.
     407             : /// 3) Otherwise, starting from the target SCC, walk all edges which reach an
     408             : ///    SCC between the source and the target, and add them to the set of
     409             : ///    connected SCCs, then recurse through them. Once a complete set of the
     410             : ///    SCCs the target connects to is known, hoist the remaining SCCs between
     411             : ///    the source and the target to be above the target. Note that there is no
     412             : ///    need to process the source SCC, it is already known to connect.
     413             : /// 4) At this point, all of the SCCs in the closed range between the source
     414             : ///    SCC and the target SCC in the postorder sequence are connected,
     415             : ///    including the target SCC and the source SCC. Inserting the edge from
     416             : ///    the source SCC to the target SCC will form a cycle out of precisely
     417             : ///    these SCCs. Thus we can merge all of the SCCs in this closed range into
     418             : ///    a single SCC.
     419             : ///
     420             : /// This process has various important properties:
     421             : /// - Only mutates the SCCs when adding the edge actually changes the SCC
     422             : ///   structure.
     423             : /// - Never mutates SCCs which are unaffected by the change.
     424             : /// - Updates the postorder sequence to correctly satisfy the postorder
     425             : ///   constraint after the edge is inserted.
     426             : /// - Only reorders SCCs in the closed postorder sequence from the source to
     427             : ///   the target, so easy to bound how much has changed even in the ordering.
     428             : /// - Big-O is the number of edges in the closed postorder range of SCCs from
     429             : ///   source to target.
     430             : ///
     431             : /// This helper routine, in addition to updating the postorder sequence itself
     432             : /// will also update a map from SCCs to indices within that sequence.
     433             : ///
     434             : /// The sequence and the map must operate on pointers to the SCC type.
     435             : ///
     436             : /// Two callbacks must be provided. The first computes the subset of SCCs in
     437             : /// the postorder closed range from the source to the target which connect to
     438             : /// the source SCC via some (transitive) set of edges. The second computes the
     439             : /// subset of the same range which the target SCC connects to via some
     440             : /// (transitive) set of edges. Both callbacks should populate the set argument
     441             : /// provided.
     442             : template <typename SCCT, typename PostorderSequenceT, typename SCCIndexMapT,
     443             :           typename ComputeSourceConnectedSetCallableT,
     444             :           typename ComputeTargetConnectedSetCallableT>
     445             : static iterator_range<typename PostorderSequenceT::iterator>
     446          31 : updatePostorderSequenceForEdgeInsertion(
     447             :     SCCT &SourceSCC, SCCT &TargetSCC, PostorderSequenceT &SCCs,
     448             :     SCCIndexMapT &SCCIndices,
     449             :     ComputeSourceConnectedSetCallableT ComputeSourceConnectedSet,
     450             :     ComputeTargetConnectedSetCallableT ComputeTargetConnectedSet) {
     451          62 :   int SourceIdx = SCCIndices[&SourceSCC];
     452          62 :   int TargetIdx = SCCIndices[&TargetSCC];
     453             :   assert(SourceIdx < TargetIdx && "Cannot have equal indices here!");
     454             : 
     455             :   SmallPtrSet<SCCT *, 4> ConnectedSet;
     456             : 
     457             :   // Compute the SCCs which (transitively) reach the source.
     458          31 :   ComputeSourceConnectedSet(ConnectedSet);
     459             : 
     460             :   // Partition the SCCs in this part of the port-order sequence so only SCCs
     461             :   // connecting to the source remain between it and the target. This is
     462             :   // a benign partition as it preserves postorder.
     463          62 :   auto SourceI = std::stable_partition(
     464          62 :       SCCs.begin() + SourceIdx, SCCs.begin() + TargetIdx + 1,
     465          77 :       [&ConnectedSet](SCCT *C) { return !ConnectedSet.count(C); });
     466         185 :   for (int i = SourceIdx, e = TargetIdx + 1; i < e; ++i)
     467         154 :     SCCIndices.find(SCCs[i])->second = i;
     468             : 
     469             :   // If the target doesn't connect to the source, then we've corrected the
     470             :   // post-order and there are no cycles formed.
     471          31 :   if (!ConnectedSet.count(&TargetSCC)) {
     472             :     assert(SourceI > (SCCs.begin() + SourceIdx) &&
     473             :            "Must have moved the source to fix the post-order.");
     474             :     assert(*std::prev(SourceI) == &TargetSCC &&
     475             :            "Last SCC to move should have bene the target.");
     476             : 
     477             :     // Return an empty range at the target SCC indicating there is nothing to
     478             :     // merge.
     479             :     return make_range(std::prev(SourceI), std::prev(SourceI));
     480             :   }
     481             : 
     482             :   assert(SCCs[TargetIdx] == &TargetSCC &&
     483             :          "Should not have moved target if connected!");
     484          54 :   SourceIdx = SourceI - SCCs.begin();
     485             :   assert(SCCs[SourceIdx] == &SourceSCC &&
     486             :          "Bad updated index computation for the source SCC!");
     487             : 
     488             : 
     489             :   // See whether there are any remaining intervening SCCs between the source
     490             :   // and target. If so we need to make sure they all are reachable form the
     491             :   // target.
     492          27 :   if (SourceIdx + 1 < TargetIdx) {
     493           7 :     ConnectedSet.clear();
     494           7 :     ComputeTargetConnectedSet(ConnectedSet);
     495             : 
     496             :     // Partition SCCs so that only SCCs reached from the target remain between
     497             :     // the source and the target. This preserves postorder.
     498          14 :     auto TargetI = std::stable_partition(
     499           7 :         SCCs.begin() + SourceIdx + 1, SCCs.begin() + TargetIdx + 1,
     500          17 :         [&ConnectedSet](SCCT *C) { return ConnectedSet.count(C); });
     501          41 :     for (int i = SourceIdx + 1, e = TargetIdx + 1; i < e; ++i)
     502          34 :       SCCIndices.find(SCCs[i])->second = i;
     503          14 :     TargetIdx = std::prev(TargetI) - SCCs.begin();
     504             :     assert(SCCs[TargetIdx] == &TargetSCC &&
     505             :            "Should always end with the target!");
     506             :   }
     507             : 
     508             :   // At this point, we know that connecting source to target forms a cycle
     509             :   // because target connects back to source, and we know that all of the SCCs
     510             :   // between the source and target in the postorder sequence participate in that
     511             :   // cycle.
     512          27 :   return make_range(SCCs.begin() + SourceIdx, SCCs.begin() + TargetIdx);
     513             : }
     514             : 
     515             : bool
     516          61 : LazyCallGraph::RefSCC::switchInternalEdgeToCall(
     517             :     Node &SourceN, Node &TargetN,
     518             :     function_ref<void(ArrayRef<SCC *> MergeSCCs)> MergeCB) {
     519             :   assert(!(*SourceN)[TargetN].isCall() && "Must start with a ref edge!");
     520             :   SmallVector<SCC *, 1> DeletedSCCs;
     521             : 
     522             : #ifndef NDEBUG
     523             :   // In a debug build, verify the RefSCC is valid to start with and when this
     524             :   // routine finishes.
     525             :   verify();
     526             :   auto VerifyOnExit = make_scope_exit([&]() { verify(); });
     527             : #endif
     528             : 
     529          61 :   SCC &SourceSCC = *G->lookupSCC(SourceN);
     530          61 :   SCC &TargetSCC = *G->lookupSCC(TargetN);
     531             : 
     532             :   // If the two nodes are already part of the same SCC, we're also done as
     533             :   // we've just added more connectivity.
     534          61 :   if (&SourceSCC == &TargetSCC) {
     535          31 :     SourceN->setEdgeKind(TargetN, Edge::Call);
     536          31 :     return false; // No new cycle.
     537             :   }
     538             : 
     539             :   // At this point we leverage the postorder list of SCCs to detect when the
     540             :   // insertion of an edge changes the SCC structure in any way.
     541             :   //
     542             :   // First and foremost, we can eliminate the need for any changes when the
     543             :   // edge is toward the beginning of the postorder sequence because all edges
     544             :   // flow in that direction already. Thus adding a new one cannot form a cycle.
     545          60 :   int SourceIdx = SCCIndices[&SourceSCC];
     546          60 :   int TargetIdx = SCCIndices[&TargetSCC];
     547          30 :   if (TargetIdx < SourceIdx) {
     548           3 :     SourceN->setEdgeKind(TargetN, Edge::Call);
     549           3 :     return false; // No new cycle.
     550             :   }
     551             : 
     552             :   // Compute the SCCs which (transitively) reach the source.
     553          27 :   auto ComputeSourceConnectedSet = [&](SmallPtrSetImpl<SCC *> &ConnectedSet) {
     554             : #ifndef NDEBUG
     555             :     // Check that the RefSCC is still valid before computing this as the
     556             :     // results will be nonsensical of we've broken its invariants.
     557             :     verify();
     558             : #endif
     559          27 :     ConnectedSet.insert(&SourceSCC);
     560          38 :     auto IsConnected = [&](SCC &C) {
     561          68 :       for (Node &N : C)
     562         232 :         for (Edge &E : N->calls())
     563         199 :           if (ConnectedSet.count(G->lookupSCC(E.getNode())))
     564          31 :             return true;
     565             : 
     566             :       return false;
     567          54 :     };
     568             : 
     569          76 :     for (SCC *C :
     570          27 :          make_range(SCCs.begin() + SourceIdx + 1, SCCs.begin() + TargetIdx + 1))
     571          38 :       if (IsConnected(*C))
     572          31 :         ConnectedSet.insert(C);
     573          54 :   };
     574             : 
     575             :   // Use a normal worklist to find which SCCs the target connects to. We still
     576             :   // bound the search based on the range in the postorder list we care about,
     577             :   // but because this is forward connectivity we just "recurse" through the
     578             :   // edges.
     579           5 :   auto ComputeTargetConnectedSet = [&](SmallPtrSetImpl<SCC *> &ConnectedSet) {
     580             : #ifndef NDEBUG
     581             :     // Check that the RefSCC is still valid before computing this as the
     582             :     // results will be nonsensical of we've broken its invariants.
     583             :     verify();
     584             : #endif
     585          10 :     ConnectedSet.insert(&TargetSCC);
     586             :     SmallVector<SCC *, 4> Worklist;
     587           5 :     Worklist.push_back(&TargetSCC);
     588             :     do {
     589             :       SCC &C = *Worklist.pop_back_val();
     590          25 :       for (Node &N : C)
     591          42 :         for (Edge &E : *N) {
     592          26 :           if (!E.isCall())
     593           2 :             continue;
     594          48 :           SCC &EdgeC = *G->lookupSCC(E.getNode());
     595          48 :           if (&EdgeC.getOuterRefSCC() != this)
     596             :             // Not in this RefSCC...
     597           0 :             continue;
     598          24 :           if (SCCIndices.find(&EdgeC)->second <= SourceIdx)
     599             :             // Not in the postorder sequence between source and target.
     600           6 :             continue;
     601             : 
     602          18 :           if (ConnectedSet.insert(&EdgeC).second)
     603           4 :             Worklist.push_back(&EdgeC);
     604             :         }
     605           9 :     } while (!Worklist.empty());
     606          32 :   };
     607             : 
     608             :   // Use a generic helper to update the postorder sequence of SCCs and return
     609             :   // a range of any SCCs connected into a cycle by inserting this edge. This
     610             :   // routine will also take care of updating the indices into the postorder
     611             :   // sequence.
     612             :   auto MergeRange = updatePostorderSequenceForEdgeInsertion(
     613             :       SourceSCC, TargetSCC, SCCs, SCCIndices, ComputeSourceConnectedSet,
     614          27 :       ComputeTargetConnectedSet);
     615             : 
     616             :   // Run the user's callback on the merged SCCs before we actually merge them.
     617          27 :   if (MergeCB)
     618             :     MergeCB(makeArrayRef(MergeRange.begin(), MergeRange.end()));
     619             : 
     620             :   // If the merge range is empty, then adding the edge didn't actually form any
     621             :   // new cycles. We're done.
     622          27 :   if (MergeRange.begin() == MergeRange.end()) {
     623             :     // Now that the SCC structure is finalized, flip the kind to call.
     624           4 :     SourceN->setEdgeKind(TargetN, Edge::Call);
     625           4 :     return false; // No new cycle.
     626             :   }
     627             : 
     628             : #ifndef NDEBUG
     629             :   // Before merging, check that the RefSCC remains valid after all the
     630             :   // postorder updates.
     631             :   verify();
     632             : #endif
     633             : 
     634             :   // Otherwise we need to merge all of the SCCs in the cycle into a single
     635             :   // result SCC.
     636             :   //
     637             :   // NB: We merge into the target because all of these functions were already
     638             :   // reachable from the target, meaning any SCC-wide properties deduced about it
     639             :   // other than the set of functions within it will not have changed.
     640          75 :   for (SCC *C : MergeRange) {
     641             :     assert(C != &TargetSCC &&
     642             :            "We merge *into* the target and shouldn't process it here!");
     643          26 :     SCCIndices.erase(C);
     644          52 :     TargetSCC.Nodes.append(C->Nodes.begin(), C->Nodes.end());
     645         104 :     for (Node *N : C->Nodes)
     646          52 :       G->SCCMap[N] = &TargetSCC;
     647          26 :     C->clear();
     648          26 :     DeletedSCCs.push_back(C);
     649             :   }
     650             : 
     651             :   // Erase the merged SCCs from the list and update the indices of the
     652             :   // remaining SCCs.
     653          23 :   int IndexOffset = MergeRange.end() - MergeRange.begin();
     654             :   auto EraseEnd = SCCs.erase(MergeRange.begin(), MergeRange.end());
     655          87 :   for (SCC *C : make_range(EraseEnd, SCCs.end()))
     656          32 :     SCCIndices[C] -= IndexOffset;
     657             : 
     658             :   // Now that the SCC structure is finalized, flip the kind to call.
     659          23 :   SourceN->setEdgeKind(TargetN, Edge::Call);
     660             : 
     661             :   // And we're done, but we did form a new cycle.
     662          23 :   return true;
     663             : }
     664             : 
     665           9 : void LazyCallGraph::RefSCC::switchTrivialInternalEdgeToRef(Node &SourceN,
     666             :                                                            Node &TargetN) {
     667             :   assert((*SourceN)[TargetN].isCall() && "Must start with a call edge!");
     668             : 
     669             : #ifndef NDEBUG
     670             :   // In a debug build, verify the RefSCC is valid to start with and when this
     671             :   // routine finishes.
     672             :   verify();
     673             :   auto VerifyOnExit = make_scope_exit([&]() { verify(); });
     674             : #endif
     675             : 
     676             :   assert(G->lookupRefSCC(SourceN) == this &&
     677             :          "Source must be in this RefSCC.");
     678             :   assert(G->lookupRefSCC(TargetN) == this &&
     679             :          "Target must be in this RefSCC.");
     680             :   assert(G->lookupSCC(SourceN) != G->lookupSCC(TargetN) &&
     681             :          "Source and Target must be in separate SCCs for this to be trivial!");
     682             : 
     683             :   // Set the edge kind.
     684           9 :   SourceN->setEdgeKind(TargetN, Edge::Ref);
     685           9 : }
     686             : 
     687             : iterator_range<LazyCallGraph::RefSCC::iterator>
     688          54 : LazyCallGraph::RefSCC::switchInternalEdgeToRef(Node &SourceN, Node &TargetN) {
     689             :   assert((*SourceN)[TargetN].isCall() && "Must start with a call edge!");
     690             : 
     691             : #ifndef NDEBUG
     692             :   // In a debug build, verify the RefSCC is valid to start with and when this
     693             :   // routine finishes.
     694             :   verify();
     695             :   auto VerifyOnExit = make_scope_exit([&]() { verify(); });
     696             : #endif
     697             : 
     698             :   assert(G->lookupRefSCC(SourceN) == this &&
     699             :          "Source must be in this RefSCC.");
     700             :   assert(G->lookupRefSCC(TargetN) == this &&
     701             :          "Target must be in this RefSCC.");
     702             : 
     703          54 :   SCC &TargetSCC = *G->lookupSCC(TargetN);
     704             :   assert(G->lookupSCC(SourceN) == &TargetSCC && "Source and Target must be in "
     705             :                                                 "the same SCC to require the "
     706             :                                                 "full CG update.");
     707             : 
     708             :   // Set the edge kind.
     709          54 :   SourceN->setEdgeKind(TargetN, Edge::Ref);
     710             : 
     711             :   // Otherwise we are removing a call edge from a single SCC. This may break
     712             :   // the cycle. In order to compute the new set of SCCs, we need to do a small
     713             :   // DFS over the nodes within the SCC to form any sub-cycles that remain as
     714             :   // distinct SCCs and compute a postorder over the resulting SCCs.
     715             :   //
     716             :   // However, we specially handle the target node. The target node is known to
     717             :   // reach all other nodes in the original SCC by definition. This means that
     718             :   // we want the old SCC to be replaced with an SCC containing that node as it
     719             :   // will be the root of whatever SCC DAG results from the DFS. Assumptions
     720             :   // about an SCC such as the set of functions called will continue to hold,
     721             :   // etc.
     722             : 
     723             :   SCC &OldSCC = TargetSCC;
     724             :   SmallVector<std::pair<Node *, EdgeSequence::call_iterator>, 16> DFSStack;
     725             :   SmallVector<Node *, 16> PendingSCCStack;
     726             :   SmallVector<SCC *, 4> NewSCCs;
     727             : 
     728             :   // Prepare the nodes for a fresh DFS.
     729             :   SmallVector<Node *, 16> Worklist;
     730          54 :   Worklist.swap(OldSCC.Nodes);
     731         696 :   for (Node *N : Worklist) {
     732         321 :     N->DFSNumber = N->LowLink = 0;
     733         321 :     G->SCCMap.erase(N);
     734             :   }
     735             : 
     736             :   // Force the target node to be in the old SCC. This also enables us to take
     737             :   // a very significant short-cut in the standard Tarjan walk to re-form SCCs
     738             :   // below: whenever we build an edge that reaches the target node, we know
     739             :   // that the target node eventually connects back to all other nodes in our
     740             :   // walk. As a consequence, we can detect and handle participants in that
     741             :   // cycle without walking all the edges that form this connection, and instead
     742             :   // by relying on the fundamental guarantee coming into this operation (all
     743             :   // nodes are reachable from the target due to previously forming an SCC).
     744          54 :   TargetN.DFSNumber = TargetN.LowLink = -1;
     745          54 :   OldSCC.Nodes.push_back(&TargetN);
     746         108 :   G->SCCMap[&TargetN] = &OldSCC;
     747             : 
     748             :   // Scan down the stack and DFS across the call edges.
     749         696 :   for (Node *RootN : Worklist) {
     750             :     assert(DFSStack.empty() &&
     751             :            "Cannot begin a new root with a non-empty DFS stack!");
     752             :     assert(PendingSCCStack.empty() &&
     753             :            "Cannot begin a new root with pending nodes for an SCC!");
     754             : 
     755             :     // Skip any nodes we've already reached in the DFS.
     756         321 :     if (RootN->DFSNumber != 0) {
     757             :       assert(RootN->DFSNumber == -1 &&
     758             :              "Shouldn't have any mid-DFS root nodes!");
     759         183 :       continue;
     760             :     }
     761             : 
     762         138 :     RootN->DFSNumber = RootN->LowLink = 1;
     763             :     int NextDFSNumber = 2;
     764             : 
     765         138 :     DFSStack.push_back({RootN, (*RootN)->call_begin()});
     766             :     do {
     767             :       Node *N;
     768             :       EdgeSequence::call_iterator I;
     769             :       std::tie(N, I) = DFSStack.pop_back_val();
     770             :       auto E = (*N)->call_end();
     771         434 :       while (I != E) {
     772             :         Node &ChildN = I->getNode();
     773         487 :         if (ChildN.DFSNumber == 0) {
     774             :           // We haven't yet visited this child, so descend, pushing the current
     775             :           // node onto the stack.
     776         129 :           DFSStack.push_back({N, I});
     777             : 
     778             :           assert(!G->SCCMap.count(&ChildN) &&
     779             :                  "Found a node with 0 DFS number but already in an SCC!");
     780         129 :           ChildN.DFSNumber = ChildN.LowLink = NextDFSNumber++;
     781         129 :           N = &ChildN;
     782         129 :           I = (*N)->call_begin();
     783             :           E = (*N)->call_end();
     784         129 :           continue;
     785             :         }
     786             : 
     787             :         // Check for the child already being part of some component.
     788         229 :         if (ChildN.DFSNumber == -1) {
     789         248 :           if (G->lookupSCC(ChildN) == &OldSCC) {
     790             :             // If the child is part of the old SCC, we know that it can reach
     791             :             // every other node, so we have formed a cycle. Pull the entire DFS
     792             :             // and pending stacks into it. See the comment above about setting
     793             :             // up the old SCC for why we do this.
     794             :             int OldSize = OldSCC.size();
     795          94 :             OldSCC.Nodes.push_back(N);
     796          94 :             OldSCC.Nodes.append(PendingSCCStack.begin(), PendingSCCStack.end());
     797             :             PendingSCCStack.clear();
     798         288 :             while (!DFSStack.empty())
     799          97 :               OldSCC.Nodes.push_back(DFSStack.pop_back_val().first);
     800         291 :             for (Node &N : make_range(OldSCC.begin() + OldSize, OldSCC.end())) {
     801         197 :               N.DFSNumber = N.LowLink = -1;
     802         394 :               G->SCCMap[&N] = &OldSCC;
     803             :             }
     804          94 :             N = nullptr;
     805          94 :             break;
     806             :           }
     807             : 
     808             :           // If the child has already been added to some child component, it
     809             :           // couldn't impact the low-link of this parent because it isn't
     810             :           // connected, and thus its low-link isn't relevant so skip it.
     811          30 :           ++I;
     812          30 :           continue;
     813             :         }
     814             : 
     815             :         // Track the lowest linked child as the lowest link for this node.
     816             :         assert(ChildN.LowLink > 0 && "Must have a positive low-link number!");
     817         105 :         if (ChildN.LowLink < N->LowLink)
     818          59 :           N->LowLink = ChildN.LowLink;
     819             : 
     820             :         // Move to the next edge.
     821         105 :         ++I;
     822             :       }
     823         170 :       if (!N)
     824             :         // Cleared the DFS early, start another round.
     825             :         break;
     826             : 
     827             :       // We've finished processing N and its descendants, put it on our pending
     828             :       // SCC stack to eventually get merged into an SCC of nodes.
     829          76 :       PendingSCCStack.push_back(N);
     830             : 
     831             :       // If this node is linked to some lower entry, continue walking up the
     832             :       // stack.
     833          76 :       if (N->LowLink != N->DFSNumber)
     834          24 :         continue;
     835             : 
     836             :       // Otherwise, we've completed an SCC. Append it to our post order list of
     837             :       // SCCs.
     838             :       int RootDFSNumber = N->DFSNumber;
     839             :       // Find the range of the node stack by walking down until we pass the
     840             :       // root DFS number.
     841             :       auto SCCNodes = make_range(
     842          52 :           PendingSCCStack.rbegin(),
     843          52 :           find_if(reverse(PendingSCCStack), [RootDFSNumber](const Node *N) {
     844             :             return N->DFSNumber < RootDFSNumber;
     845             :           }));
     846             : 
     847             :       // Form a new SCC out of these nodes and then clear them off our pending
     848             :       // stack.
     849          52 :       NewSCCs.push_back(G->createSCC(*this, SCCNodes));
     850         174 :       for (Node &N : *NewSCCs.back()) {
     851          70 :         N.DFSNumber = N.LowLink = -1;
     852         140 :         G->SCCMap[&N] = NewSCCs.back();
     853             :       }
     854             :       PendingSCCStack.erase(SCCNodes.end().base(), PendingSCCStack.end());
     855          76 :     } while (!DFSStack.empty());
     856             :   }
     857             : 
     858             :   // Insert the remaining SCCs before the old one. The old SCC can reach all
     859             :   // other SCCs we form because it contains the target node of the removed edge
     860             :   // of the old SCC. This means that we will have edges into all of the new
     861             :   // SCCs, which means the old one must come last for postorder.
     862         108 :   int OldIdx = SCCIndices[&OldSCC];
     863         108 :   SCCs.insert(SCCs.begin() + OldIdx, NewSCCs.begin(), NewSCCs.end());
     864             : 
     865             :   // Update the mapping from SCC* to index to use the new SCC*s, and remove the
     866             :   // old SCC from the mapping.
     867         163 :   for (int Idx = OldIdx, Size = SCCs.size(); Idx < Size; ++Idx)
     868         218 :     SCCIndices[SCCs[Idx]] = Idx;
     869             : 
     870             :   return make_range(SCCs.begin() + OldIdx,
     871         108 :                     SCCs.begin() + OldIdx + NewSCCs.size());
     872             : }
     873             : 
     874           4 : void LazyCallGraph::RefSCC::switchOutgoingEdgeToCall(Node &SourceN,
     875             :                                                      Node &TargetN) {
     876             :   assert(!(*SourceN)[TargetN].isCall() && "Must start with a ref edge!");
     877             : 
     878             :   assert(G->lookupRefSCC(SourceN) == this && "Source must be in this RefSCC.");
     879             :   assert(G->lookupRefSCC(TargetN) != this &&
     880             :          "Target must not be in this RefSCC.");
     881             : #ifdef EXPENSIVE_CHECKS
     882             :   assert(G->lookupRefSCC(TargetN)->isDescendantOf(*this) &&
     883             :          "Target must be a descendant of the Source.");
     884             : #endif
     885             : 
     886             :   // Edges between RefSCCs are the same regardless of call or ref, so we can
     887             :   // just flip the edge here.
     888           4 :   SourceN->setEdgeKind(TargetN, Edge::Call);
     889             : 
     890             : #ifndef NDEBUG
     891             :   // Check that the RefSCC is still valid.
     892             :   verify();
     893             : #endif
     894           4 : }
     895             : 
     896           6 : void LazyCallGraph::RefSCC::switchOutgoingEdgeToRef(Node &SourceN,
     897             :                                                     Node &TargetN) {
     898             :   assert((*SourceN)[TargetN].isCall() && "Must start with a call edge!");
     899             : 
     900             :   assert(G->lookupRefSCC(SourceN) == this && "Source must be in this RefSCC.");
     901             :   assert(G->lookupRefSCC(TargetN) != this &&
     902             :          "Target must not be in this RefSCC.");
     903             : #ifdef EXPENSIVE_CHECKS
     904             :   assert(G->lookupRefSCC(TargetN)->isDescendantOf(*this) &&
     905             :          "Target must be a descendant of the Source.");
     906             : #endif
     907             : 
     908             :   // Edges between RefSCCs are the same regardless of call or ref, so we can
     909             :   // just flip the edge here.
     910           6 :   SourceN->setEdgeKind(TargetN, Edge::Ref);
     911             : 
     912             : #ifndef NDEBUG
     913             :   // Check that the RefSCC is still valid.
     914             :   verify();
     915             : #endif
     916           6 : }
     917             : 
     918           1 : void LazyCallGraph::RefSCC::insertInternalRefEdge(Node &SourceN,
     919             :                                                   Node &TargetN) {
     920             :   assert(G->lookupRefSCC(SourceN) == this && "Source must be in this RefSCC.");
     921             :   assert(G->lookupRefSCC(TargetN) == this && "Target must be in this RefSCC.");
     922             : 
     923           1 :   SourceN->insertEdgeInternal(TargetN, Edge::Ref);
     924             : 
     925             : #ifndef NDEBUG
     926             :   // Check that the RefSCC is still valid.
     927             :   verify();
     928             : #endif
     929           1 : }
     930             : 
     931           1 : void LazyCallGraph::RefSCC::insertOutgoingEdge(Node &SourceN, Node &TargetN,
     932             :                                                Edge::Kind EK) {
     933             :   // First insert it into the caller.
     934           1 :   SourceN->insertEdgeInternal(TargetN, EK);
     935             : 
     936             :   assert(G->lookupRefSCC(SourceN) == this && "Source must be in this RefSCC.");
     937             : 
     938             :   assert(G->lookupRefSCC(TargetN) != this &&
     939             :          "Target must not be in this RefSCC.");
     940             : #ifdef EXPENSIVE_CHECKS
     941             :   assert(G->lookupRefSCC(TargetN)->isDescendantOf(*this) &&
     942             :          "Target must be a descendant of the Source.");
     943             : #endif
     944             : 
     945             : #ifndef NDEBUG
     946             :   // Check that the RefSCC is still valid.
     947             :   verify();
     948             : #endif
     949           1 : }
     950             : 
     951             : SmallVector<LazyCallGraph::RefSCC *, 1>
     952           4 : LazyCallGraph::RefSCC::insertIncomingRefEdge(Node &SourceN, Node &TargetN) {
     953             :   assert(G->lookupRefSCC(TargetN) == this && "Target must be in this RefSCC.");
     954           4 :   RefSCC &SourceC = *G->lookupRefSCC(SourceN);
     955             :   assert(&SourceC != this && "Source must not be in this RefSCC.");
     956             : #ifdef EXPENSIVE_CHECKS
     957             :   assert(SourceC.isDescendantOf(*this) &&
     958             :          "Source must be a descendant of the Target.");
     959             : #endif
     960             : 
     961             :   SmallVector<RefSCC *, 1> DeletedRefSCCs;
     962             : 
     963             : #ifndef NDEBUG
     964             :   // In a debug build, verify the RefSCC is valid to start with and when this
     965             :   // routine finishes.
     966             :   verify();
     967             :   auto VerifyOnExit = make_scope_exit([&]() { verify(); });
     968             : #endif
     969             : 
     970           8 :   int SourceIdx = G->RefSCCIndices[&SourceC];
     971           8 :   int TargetIdx = G->RefSCCIndices[this];
     972             :   assert(SourceIdx < TargetIdx &&
     973             :          "Postorder list doesn't see edge as incoming!");
     974             : 
     975             :   // Compute the RefSCCs which (transitively) reach the source. We do this by
     976             :   // working backwards from the source using the parent set in each RefSCC,
     977             :   // skipping any RefSCCs that don't fall in the postorder range. This has the
     978             :   // advantage of walking the sparser parent edge (in high fan-out graphs) but
     979             :   // more importantly this removes examining all forward edges in all RefSCCs
     980             :   // within the postorder range which aren't in fact connected. Only connected
     981             :   // RefSCCs (and their edges) are visited here.
     982           4 :   auto ComputeSourceConnectedSet = [&](SmallPtrSetImpl<RefSCC *> &Set) {
     983           4 :     Set.insert(&SourceC);
     984           8 :     auto IsConnected = [&](RefSCC &RC) {
     985           9 :       for (SCC &C : RC)
     986          11 :         for (Node &N : C)
     987          13 :           for (Edge &E : *N)
     988          26 :             if (Set.count(G->lookupRefSCC(E.getNode())))
     989             :               return true;
     990             : 
     991             :       return false;
     992           8 :     };
     993             : 
     994          20 :     for (RefSCC *C : make_range(G->PostOrderRefSCCs.begin() + SourceIdx + 1,
     995          12 :                                 G->PostOrderRefSCCs.begin() + TargetIdx + 1))
     996           8 :       if (IsConnected(*C))
     997           8 :         Set.insert(C);
     998           8 :   };
     999             : 
    1000             :   // Use a normal worklist to find which SCCs the target connects to. We still
    1001             :   // bound the search based on the range in the postorder list we care about,
    1002             :   // but because this is forward connectivity we just "recurse" through the
    1003             :   // edges.
    1004           2 :   auto ComputeTargetConnectedSet = [&](SmallPtrSetImpl<RefSCC *> &Set) {
    1005          16 :     Set.insert(this);
    1006             :     SmallVector<RefSCC *, 4> Worklist;
    1007           2 :     Worklist.push_back(this);
    1008             :     do {
    1009             :       RefSCC &RC = *Worklist.pop_back_val();
    1010          12 :       for (SCC &C : RC)
    1011          12 :         for (Node &N : C)
    1012          12 :           for (Edge &E : *N) {
    1013          12 :             RefSCC &EdgeRC = *G->lookupRefSCC(E.getNode());
    1014          12 :             if (G->getRefSCCIndex(EdgeRC) <= SourceIdx)
    1015             :               // Not in the postorder sequence between source and target.
    1016           2 :               continue;
    1017             : 
    1018           4 :             if (Set.insert(&EdgeRC).second)
    1019           4 :               Worklist.push_back(&EdgeRC);
    1020             :           }
    1021           6 :     } while (!Worklist.empty());
    1022           6 :   };
    1023             : 
    1024             :   // Use a generic helper to update the postorder sequence of RefSCCs and return
    1025             :   // a range of any RefSCCs connected into a cycle by inserting this edge. This
    1026             :   // routine will also take care of updating the indices into the postorder
    1027             :   // sequence.
    1028             :   iterator_range<SmallVectorImpl<RefSCC *>::iterator> MergeRange =
    1029             :       updatePostorderSequenceForEdgeInsertion(
    1030           4 :           SourceC, *this, G->PostOrderRefSCCs, G->RefSCCIndices,
    1031           4 :           ComputeSourceConnectedSet, ComputeTargetConnectedSet);
    1032             : 
    1033             :   // Build a set so we can do fast tests for whether a RefSCC will end up as
    1034             :   // part of the merged RefSCC.
    1035           4 :   SmallPtrSet<RefSCC *, 16> MergeSet(MergeRange.begin(), MergeRange.end());
    1036             : 
    1037             :   // This RefSCC will always be part of that set, so just insert it here.
    1038           4 :   MergeSet.insert(this);
    1039             : 
    1040             :   // Now that we have identified all of the SCCs which need to be merged into
    1041             :   // a connected set with the inserted edge, merge all of them into this SCC.
    1042             :   SmallVector<SCC *, 16> MergedSCCs;
    1043             :   int SCCIndex = 0;
    1044          20 :   for (RefSCC *RC : MergeRange) {
    1045             :     assert(RC != this && "We're merging into the target RefSCC, so it "
    1046             :                          "shouldn't be in the range.");
    1047             : 
    1048             :     // Walk the inner SCCs to update their up-pointer and walk all the edges to
    1049             :     // update any parent sets.
    1050             :     // FIXME: We should try to find a way to avoid this (rather expensive) edge
    1051             :     // walk by updating the parent sets in some other manner.
    1052          18 :     for (SCC &InnerC : *RC) {
    1053          10 :       InnerC.OuterRefSCC = this;
    1054          20 :       SCCIndices[&InnerC] = SCCIndex++;
    1055          22 :       for (Node &N : InnerC)
    1056          24 :         G->SCCMap[&N] = &InnerC;
    1057             :     }
    1058             : 
    1059             :     // Now merge in the SCCs. We can actually move here so try to reuse storage
    1060             :     // the first time through.
    1061           8 :     if (MergedSCCs.empty())
    1062           4 :       MergedSCCs = std::move(RC->SCCs);
    1063             :     else
    1064           8 :       MergedSCCs.append(RC->SCCs.begin(), RC->SCCs.end());
    1065           8 :     RC->SCCs.clear();
    1066           8 :     DeletedRefSCCs.push_back(RC);
    1067             :   }
    1068             : 
    1069             :   // Append our original SCCs to the merged list and move it into place.
    1070          10 :   for (SCC &InnerC : *this)
    1071          12 :     SCCIndices[&InnerC] = SCCIndex++;
    1072           4 :   MergedSCCs.append(SCCs.begin(), SCCs.end());
    1073             :   SCCs = std::move(MergedSCCs);
    1074             : 
    1075             :   // Remove the merged away RefSCCs from the post order sequence.
    1076          20 :   for (RefSCC *RC : MergeRange)
    1077           8 :     G->RefSCCIndices.erase(RC);
    1078           4 :   int IndexOffset = MergeRange.end() - MergeRange.begin();
    1079             :   auto EraseEnd =
    1080           4 :       G->PostOrderRefSCCs.erase(MergeRange.begin(), MergeRange.end());
    1081          24 :   for (RefSCC *RC : make_range(EraseEnd, G->PostOrderRefSCCs.end()))
    1082          16 :     G->RefSCCIndices[RC] -= IndexOffset;
    1083             : 
    1084             :   // At this point we have a merged RefSCC with a post-order SCCs list, just
    1085             :   // connect the nodes to form the new edge.
    1086           4 :   SourceN->insertEdgeInternal(TargetN, Edge::Ref);
    1087             : 
    1088             :   // We return the list of SCCs which were merged so that callers can
    1089             :   // invalidate any data they have associated with those SCCs. Note that these
    1090             :   // SCCs are no longer in an interesting state (they are totally empty) but
    1091             :   // the pointers will remain stable for the life of the graph itself.
    1092           4 :   return DeletedRefSCCs;
    1093             : }
    1094             : 
    1095         281 : void LazyCallGraph::RefSCC::removeOutgoingEdge(Node &SourceN, Node &TargetN) {
    1096             :   assert(G->lookupRefSCC(SourceN) == this &&
    1097             :          "The source must be a member of this RefSCC.");
    1098             :   assert(G->lookupRefSCC(TargetN) != this &&
    1099             :          "The target must not be a member of this RefSCC");
    1100             : 
    1101             : #ifndef NDEBUG
    1102             :   // In a debug build, verify the RefSCC is valid to start with and when this
    1103             :   // routine finishes.
    1104             :   verify();
    1105             :   auto VerifyOnExit = make_scope_exit([&]() { verify(); });
    1106             : #endif
    1107             : 
    1108             :   // First remove it from the node.
    1109         281 :   bool Removed = SourceN->removeEdgeInternal(TargetN);
    1110             :   (void)Removed;
    1111             :   assert(Removed && "Target not in the edge set for this caller?");
    1112         281 : }
    1113             : 
    1114             : SmallVector<LazyCallGraph::RefSCC *, 1>
    1115         441 : LazyCallGraph::RefSCC::removeInternalRefEdge(Node &SourceN,
    1116             :                                              ArrayRef<Node *> TargetNs) {
    1117             :   // We return a list of the resulting *new* RefSCCs in post-order.
    1118             :   SmallVector<RefSCC *, 1> Result;
    1119             : 
    1120             : #ifndef NDEBUG
    1121             :   // In a debug build, verify the RefSCC is valid to start with and that either
    1122             :   // we return an empty list of result RefSCCs and this RefSCC remains valid,
    1123             :   // or we return new RefSCCs and this RefSCC is dead.
    1124             :   verify();
    1125             :   auto VerifyOnExit = make_scope_exit([&]() {
    1126             :     // If we didn't replace our RefSCC with new ones, check that this one
    1127             :     // remains valid.
    1128             :     if (G)
    1129             :       verify();
    1130             :   });
    1131             : #endif
    1132             : 
    1133             :   // First remove the actual edges.
    1134         551 :   for (Node *TargetN : TargetNs) {
    1135             :     assert(!(*SourceN)[*TargetN].isCall() &&
    1136             :            "Cannot remove a call edge, it must first be made a ref edge");
    1137             : 
    1138          55 :     bool Removed = SourceN->removeEdgeInternal(*TargetN);
    1139             :     (void)Removed;
    1140             :     assert(Removed && "Target not in the edge set for this caller?");
    1141             :   }
    1142             : 
    1143             :   // Direct self references don't impact the ref graph at all.
    1144         441 :   if (llvm::all_of(TargetNs,
    1145             :                    [&](Node *TargetN) { return &SourceN == TargetN; }))
    1146             :     return Result;
    1147             : 
    1148             :   // If all targets are in the same SCC as the source, because no call edges
    1149             :   // were removed there is no RefSCC structure change.
    1150          39 :   SCC &SourceC = *G->lookupSCC(SourceN);
    1151          78 :   if (llvm::all_of(TargetNs, [&](Node *TargetN) {
    1152          78 :         return G->lookupSCC(*TargetN) == &SourceC;
    1153          39 :       }))
    1154             :     return Result;
    1155             : 
    1156             :   // We build somewhat synthetic new RefSCCs by providing a postorder mapping
    1157             :   // for each inner SCC. We store these inside the low-link field of the nodes
    1158             :   // rather than associated with SCCs because this saves a round-trip through
    1159             :   // the node->SCC map and in the common case, SCCs are small. We will verify
    1160             :   // that we always give the same number to every node in the SCC such that
    1161             :   // these are equivalent.
    1162             :   int PostOrderNumber = 0;
    1163             : 
    1164             :   // Reset all the other nodes to prepare for a DFS over them, and add them to
    1165             :   // our worklist.
    1166             :   SmallVector<Node *, 8> Worklist;
    1167         179 :   for (SCC *C : SCCs) {
    1168         240 :     for (Node &N : *C)
    1169         166 :       N.DFSNumber = N.LowLink = 0;
    1170             : 
    1171          74 :     Worklist.append(C->Nodes.begin(), C->Nodes.end());
    1172             :   }
    1173             : 
    1174             :   // Track the number of nodes in this RefSCC so that we can quickly recognize
    1175             :   // an important special case of the edge removal not breaking the cycle of
    1176             :   // this RefSCC.
    1177          31 :   const int NumRefSCCNodes = Worklist.size();
    1178             : 
    1179             :   SmallVector<std::pair<Node *, EdgeSequence::iterator>, 4> DFSStack;
    1180             :   SmallVector<Node *, 4> PendingRefSCCStack;
    1181             :   do {
    1182             :     assert(DFSStack.empty() &&
    1183             :            "Cannot begin a new root with a non-empty DFS stack!");
    1184             :     assert(PendingRefSCCStack.empty() &&
    1185             :            "Cannot begin a new root with pending nodes for an SCC!");
    1186             : 
    1187             :     Node *RootN = Worklist.pop_back_val();
    1188             :     // Skip any nodes we've already reached in the DFS.
    1189          92 :     if (RootN->DFSNumber != 0) {
    1190             :       assert(RootN->DFSNumber == -1 &&
    1191             :              "Shouldn't have any mid-DFS root nodes!");
    1192             :       continue;
    1193             :     }
    1194             : 
    1195          33 :     RootN->DFSNumber = RootN->LowLink = 1;
    1196             :     int NextDFSNumber = 2;
    1197             : 
    1198          33 :     DFSStack.push_back({RootN, (*RootN)->begin()});
    1199             :     do {
    1200             :       Node *N;
    1201             :       EdgeSequence::iterator I;
    1202             :       std::tie(N, I) = DFSStack.pop_back_val();
    1203             :       auto E = (*N)->end();
    1204             : 
    1205             :       assert(N->DFSNumber != 0 && "We should always assign a DFS number "
    1206             :                                   "before processing a node.");
    1207             : 
    1208         617 :       while (I != E) {
    1209             :         Node &ChildN = I->getNode();
    1210         584 :         if (ChildN.DFSNumber == 0) {
    1211             :           // Mark that we should start at this child when next this node is the
    1212             :           // top of the stack. We don't start at the next child to ensure this
    1213             :           // child's lowlink is reflected.
    1214         133 :           DFSStack.push_back({N, I});
    1215             : 
    1216             :           // Continue, resetting to the child node.
    1217         133 :           ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
    1218         133 :           N = &ChildN;
    1219         133 :           I = ChildN->begin();
    1220             :           E = ChildN->end();
    1221         133 :           continue;
    1222             :         }
    1223         366 :         if (ChildN.DFSNumber == -1) {
    1224             :           // If this child isn't currently in this RefSCC, no need to process
    1225             :           // it.
    1226             :           ++I;
    1227          48 :           continue;
    1228             :         }
    1229             : 
    1230             :         // Track the lowest link of the children, if any are still in the stack.
    1231             :         // Any child not on the stack will have a LowLink of -1.
    1232             :         assert(ChildN.LowLink != 0 &&
    1233             :                "Low-link must not be zero with a non-zero DFS number.");
    1234         270 :         if (ChildN.LowLink >= 0 && ChildN.LowLink < N->LowLink)
    1235         144 :           N->LowLink = ChildN.LowLink;
    1236             :         ++I;
    1237             :       }
    1238             : 
    1239             :       // We've finished processing N and its descendants, put it on our pending
    1240             :       // stack to eventually get merged into a RefSCC.
    1241         166 :       PendingRefSCCStack.push_back(N);
    1242             : 
    1243             :       // If this node is linked to some lower entry, continue walking up the
    1244             :       // stack.
    1245         166 :       if (N->LowLink != N->DFSNumber) {
    1246             :         assert(!DFSStack.empty() &&
    1247             :                "We never found a viable root for a RefSCC to pop off!");
    1248         107 :         continue;
    1249             :       }
    1250             : 
    1251             :       // Otherwise, form a new RefSCC from the top of the pending node stack.
    1252          59 :       int RefSCCNumber = PostOrderNumber++;
    1253          59 :       int RootDFSNumber = N->DFSNumber;
    1254             : 
    1255             :       // Find the range of the node stack by walking down until we pass the
    1256             :       // root DFS number. Update the DFS numbers and low link numbers in the
    1257             :       // process to avoid re-walking this list where possible.
    1258             :       auto StackRI = find_if(reverse(PendingRefSCCStack), [&](Node *N) {
    1259         170 :         if (N->DFSNumber < RootDFSNumber)
    1260             :           // We've found the bottom.
    1261             :           return true;
    1262             : 
    1263             :         // Update this node and keep scanning.
    1264         166 :         N->DFSNumber = -1;
    1265             :         // Save the post-order number in the lowlink field so that we can use
    1266             :         // it to map SCCs into new RefSCCs after we finish the DFS.
    1267         166 :         N->LowLink = RefSCCNumber;
    1268             :         return false;
    1269             :       });
    1270             :       auto RefSCCNodes = make_range(StackRI.base(), PendingRefSCCStack.end());
    1271             : 
    1272             :       // If we find a cycle containing all nodes originally in this RefSCC then
    1273             :       // the removal hasn't changed the structure at all. This is an important
    1274             :       // special case and we can directly exit the entire routine more
    1275             :       // efficiently as soon as we discover it.
    1276          59 :       if (llvm::size(RefSCCNodes) == NumRefSCCNodes) {
    1277             :         // Clear out the low link field as we won't need it.
    1278         175 :         for (Node *N : RefSCCNodes)
    1279          83 :           N->LowLink = -1;
    1280             :         // Return the empty result immediately.
    1281           9 :         return Result;
    1282             :       }
    1283             : 
    1284             :       // We've already marked the nodes internally with the RefSCC number so
    1285             :       // just clear them off the stack and continue.
    1286             :       PendingRefSCCStack.erase(RefSCCNodes.begin(), PendingRefSCCStack.end());
    1287         157 :     } while (!DFSStack.empty());
    1288             : 
    1289             :     assert(DFSStack.empty() && "Didn't flush the entire DFS stack!");
    1290             :     assert(PendingRefSCCStack.empty() && "Didn't flush all pending nodes!");
    1291          83 :   } while (!Worklist.empty());
    1292             : 
    1293             :   assert(PostOrderNumber > 1 &&
    1294             :          "Should never finish the DFS when the existing RefSCC remains valid!");
    1295             : 
    1296             :   // Otherwise we create a collection of new RefSCC nodes and build
    1297             :   // a radix-sort style map from postorder number to these new RefSCCs. We then
    1298             :   // append SCCs to each of these RefSCCs in the order they occurred in the
    1299             :   // original SCCs container.
    1300         122 :   for (int i = 0; i < PostOrderNumber; ++i)
    1301         100 :     Result.push_back(G->createRefSCC(*G));
    1302             : 
    1303             :   // Insert the resulting postorder sequence into the global graph postorder
    1304             :   // sequence before the current RefSCC in that sequence, and then remove the
    1305             :   // current one.
    1306             :   //
    1307             :   // FIXME: It'd be nice to change the APIs so that we returned an iterator
    1308             :   // range over the global postorder sequence and generally use that sequence
    1309             :   // rather than building a separate result vector here.
    1310          22 :   int Idx = G->getRefSCCIndex(*this);
    1311          44 :   G->PostOrderRefSCCs.erase(G->PostOrderRefSCCs.begin() + Idx);
    1312          44 :   G->PostOrderRefSCCs.insert(G->PostOrderRefSCCs.begin() + Idx, Result.begin(),
    1313             :                              Result.end());
    1314          44 :   for (int i : seq<int>(Idx, G->PostOrderRefSCCs.size()))
    1315         264 :     G->RefSCCIndices[G->PostOrderRefSCCs[i]] = i;
    1316             : 
    1317         130 :   for (SCC *C : SCCs) {
    1318             :     // We store the SCC number in the node's low-link field above.
    1319          54 :     int SCCNumber = C->begin()->LowLink;
    1320             :     // Clear out all of the SCC's node's low-link fields now that we're done
    1321             :     // using them as side-storage.
    1322         137 :     for (Node &N : *C) {
    1323             :       assert(N.LowLink == SCCNumber &&
    1324             :              "Cannot have different numbers for nodes in the same SCC!");
    1325          83 :       N.LowLink = -1;
    1326             :     }
    1327             : 
    1328         108 :     RefSCC &RC = *Result[SCCNumber];
    1329          54 :     int SCCIndex = RC.SCCs.size();
    1330          54 :     RC.SCCs.push_back(C);
    1331         108 :     RC.SCCIndices[C] = SCCIndex;
    1332          54 :     C->OuterRefSCC = &RC;
    1333             :   }
    1334             : 
    1335             :   // Now that we've moved things into the new RefSCCs, clear out our current
    1336             :   // one.
    1337          22 :   G = nullptr;
    1338             :   SCCs.clear();
    1339          22 :   SCCIndices.clear();
    1340             : 
    1341             : #ifndef NDEBUG
    1342             :   // Verify the new RefSCCs we've built.
    1343             :   for (RefSCC *RC : Result)
    1344             :     RC->verify();
    1345             : #endif
    1346             : 
    1347             :   // Return the new list of SCCs.
    1348          22 :   return Result;
    1349             : }
    1350             : 
    1351          56 : void LazyCallGraph::RefSCC::handleTrivialEdgeInsertion(Node &SourceN,
    1352             :                                                        Node &TargetN) {
    1353             :   // The only trivial case that requires any graph updates is when we add new
    1354             :   // ref edge and may connect different RefSCCs along that path. This is only
    1355             :   // because of the parents set. Every other part of the graph remains constant
    1356             :   // after this edge insertion.
    1357             :   assert(G->lookupRefSCC(SourceN) == this && "Source must be in this RefSCC.");
    1358          56 :   RefSCC &TargetRC = *G->lookupRefSCC(TargetN);
    1359             :   if (&TargetRC == this)
    1360             :     return;
    1361             : 
    1362             : #ifdef EXPENSIVE_CHECKS
    1363             :   assert(TargetRC.isDescendantOf(*this) &&
    1364             :          "Target must be a descendant of the Source.");
    1365             : #endif
    1366             : }
    1367             : 
    1368           2 : void LazyCallGraph::RefSCC::insertTrivialCallEdge(Node &SourceN,
    1369             :                                                   Node &TargetN) {
    1370             : #ifndef NDEBUG
    1371             :   // Check that the RefSCC is still valid when we finish.
    1372             :   auto ExitVerifier = make_scope_exit([this] { verify(); });
    1373             : 
    1374             : #ifdef EXPENSIVE_CHECKS
    1375             :   // Check that we aren't breaking some invariants of the SCC graph. Note that
    1376             :   // this is quadratic in the number of edges in the call graph!
    1377             :   SCC &SourceC = *G->lookupSCC(SourceN);
    1378             :   SCC &TargetC = *G->lookupSCC(TargetN);
    1379             :   if (&SourceC != &TargetC)
    1380             :     assert(SourceC.isAncestorOf(TargetC) &&
    1381             :            "Call edge is not trivial in the SCC graph!");
    1382             : #endif // EXPENSIVE_CHECKS
    1383             : #endif // NDEBUG
    1384             : 
    1385             :   // First insert it into the source or find the existing edge.
    1386             :   auto InsertResult =
    1387           4 :       SourceN->EdgeIndexMap.insert({&TargetN, SourceN->Edges.size()});
    1388           2 :   if (!InsertResult.second) {
    1389             :     // Already an edge, just update it.
    1390           0 :     Edge &E = SourceN->Edges[InsertResult.first->second];
    1391           0 :     if (E.isCall())
    1392           0 :       return; // Nothing to do!
    1393             :     E.setKind(Edge::Call);
    1394             :   } else {
    1395             :     // Create the new edge.
    1396           2 :     SourceN->Edges.emplace_back(TargetN, Edge::Call);
    1397             :   }
    1398             : 
    1399             :   // Now that we have the edge, handle the graph fallout.
    1400           2 :   handleTrivialEdgeInsertion(SourceN, TargetN);
    1401             : }
    1402             : 
    1403          76 : void LazyCallGraph::RefSCC::insertTrivialRefEdge(Node &SourceN, Node &TargetN) {
    1404             : #ifndef NDEBUG
    1405             :   // Check that the RefSCC is still valid when we finish.
    1406             :   auto ExitVerifier = make_scope_exit([this] { verify(); });
    1407             : 
    1408             : #ifdef EXPENSIVE_CHECKS
    1409             :   // Check that we aren't breaking some invariants of the RefSCC graph.
    1410             :   RefSCC &SourceRC = *G->lookupRefSCC(SourceN);
    1411             :   RefSCC &TargetRC = *G->lookupRefSCC(TargetN);
    1412             :   if (&SourceRC != &TargetRC)
    1413             :     assert(SourceRC.isAncestorOf(TargetRC) &&
    1414             :            "Ref edge is not trivial in the RefSCC graph!");
    1415             : #endif // EXPENSIVE_CHECKS
    1416             : #endif // NDEBUG
    1417             : 
    1418             :   // First insert it into the source or find the existing edge.
    1419             :   auto InsertResult =
    1420         152 :       SourceN->EdgeIndexMap.insert({&TargetN, SourceN->Edges.size()});
    1421          76 :   if (!InsertResult.second)
    1422             :     // Already an edge, we're done.
    1423          22 :     return;
    1424             : 
    1425             :   // Create the new edge.
    1426          54 :   SourceN->Edges.emplace_back(TargetN, Edge::Ref);
    1427             : 
    1428             :   // Now that we have the edge, handle the graph fallout.
    1429          54 :   handleTrivialEdgeInsertion(SourceN, TargetN);
    1430             : }
    1431             : 
    1432          20 : void LazyCallGraph::RefSCC::replaceNodeFunction(Node &N, Function &NewF) {
    1433          20 :   Function &OldF = N.getFunction();
    1434             : 
    1435             : #ifndef NDEBUG
    1436             :   // Check that the RefSCC is still valid when we finish.
    1437             :   auto ExitVerifier = make_scope_exit([this] { verify(); });
    1438             : 
    1439             :   assert(G->lookupRefSCC(N) == this &&
    1440             :          "Cannot replace the function of a node outside this RefSCC.");
    1441             : 
    1442             :   assert(G->NodeMap.find(&NewF) == G->NodeMap.end() &&
    1443             :          "Must not have already walked the new function!'");
    1444             : 
    1445             :   // It is important that this replacement not introduce graph changes so we
    1446             :   // insist that the caller has already removed every use of the original
    1447             :   // function and that all uses of the new function correspond to existing
    1448             :   // edges in the graph. The common and expected way to use this is when
    1449             :   // replacing the function itself in the IR without changing the call graph
    1450             :   // shape and just updating the analysis based on that.
    1451             :   assert(&OldF != &NewF && "Cannot replace a function with itself!");
    1452             :   assert(OldF.use_empty() &&
    1453             :          "Must have moved all uses from the old function to the new!");
    1454             : #endif
    1455             : 
    1456          20 :   N.replaceFunction(NewF);
    1457             : 
    1458             :   // Update various call graph maps.
    1459          20 :   G->NodeMap.erase(&OldF);
    1460          40 :   G->NodeMap[&NewF] = &N;
    1461          20 : }
    1462             : 
    1463           8 : void LazyCallGraph::insertEdge(Node &SourceN, Node &TargetN, Edge::Kind EK) {
    1464             :   assert(SCCMap.empty() &&
    1465             :          "This method cannot be called after SCCs have been formed!");
    1466             : 
    1467           8 :   return SourceN->insertEdgeInternal(TargetN, EK);
    1468             : }
    1469             : 
    1470           3 : void LazyCallGraph::removeEdge(Node &SourceN, Node &TargetN) {
    1471             :   assert(SCCMap.empty() &&
    1472             :          "This method cannot be called after SCCs have been formed!");
    1473             : 
    1474           3 :   bool Removed = SourceN->removeEdgeInternal(TargetN);
    1475             :   (void)Removed;
    1476             :   assert(Removed && "Target not in the edge set for this caller?");
    1477           3 : }
    1478             : 
    1479          87 : void LazyCallGraph::removeDeadFunction(Function &F) {
    1480             :   // FIXME: This is unnecessarily restrictive. We should be able to remove
    1481             :   // functions which recursively call themselves.
    1482             :   assert(F.use_empty() &&
    1483             :          "This routine should only be called on trivially dead functions!");
    1484             : 
    1485             :   // We shouldn't remove library functions as they are never really dead while
    1486             :   // the call graph is in use -- every function definition refers to them.
    1487             :   assert(!isLibFunction(F) &&
    1488             :          "Must not remove lib functions from the call graph!");
    1489             : 
    1490          87 :   auto NI = NodeMap.find(&F);
    1491          87 :   if (NI == NodeMap.end())
    1492             :     // Not in the graph at all!
    1493           0 :     return;
    1494             : 
    1495          87 :   Node &N = *NI->second;
    1496             :   NodeMap.erase(NI);
    1497             : 
    1498             :   // Remove this from the entry edges if present.
    1499          87 :   EntryEdges.removeEdgeInternal(N);
    1500             : 
    1501          87 :   if (SCCMap.empty()) {
    1502             :     // No SCCs have been formed, so removing this is fine and there is nothing
    1503             :     // else necessary at this point but clearing out the node.
    1504             :     N.clear();
    1505             :     return;
    1506             :   }
    1507             : 
    1508             :   // Cannot remove a function which has yet to be visited in the DFS walk, so
    1509             :   // if we have a node at all then we must have an SCC and RefSCC.
    1510          87 :   auto CI = SCCMap.find(&N);
    1511             :   assert(CI != SCCMap.end() &&
    1512             :          "Tried to remove a node without an SCC after DFS walk started!");
    1513          87 :   SCC &C = *CI->second;
    1514             :   SCCMap.erase(CI);
    1515          87 :   RefSCC &RC = C.getOuterRefSCC();
    1516             : 
    1517             :   // This node must be the only member of its SCC as it has no callers, and
    1518             :   // that SCC must be the only member of a RefSCC as it has no references.
    1519             :   // Validate these properties first.
    1520             :   assert(C.size() == 1 && "Dead functions must be in a singular SCC");
    1521             :   assert(RC.size() == 1 && "Dead functions must be in a singular RefSCC");
    1522             : 
    1523          87 :   auto RCIndexI = RefSCCIndices.find(&RC);
    1524          87 :   int RCIndex = RCIndexI->second;
    1525         174 :   PostOrderRefSCCs.erase(PostOrderRefSCCs.begin() + RCIndex);
    1526             :   RefSCCIndices.erase(RCIndexI);
    1527         675 :   for (int i = RCIndex, Size = PostOrderRefSCCs.size(); i < Size; ++i)
    1528        1176 :     RefSCCIndices[PostOrderRefSCCs[i]] = i;
    1529             : 
    1530             :   // Finally clear out all the data structures from the node down through the
    1531             :   // components.
    1532             :   N.clear();
    1533          87 :   N.G = nullptr;
    1534          87 :   N.F = nullptr;
    1535             :   C.clear();
    1536             :   RC.clear();
    1537          87 :   RC.G = nullptr;
    1538             : 
    1539             :   // Nothing to delete as all the objects are allocated in stable bump pointer
    1540             :   // allocators.
    1541             : }
    1542             : 
    1543        1188 : LazyCallGraph::Node &LazyCallGraph::insertInto(Function &F, Node *&MappedN) {
    1544        2376 :   return *new (MappedN = BPA.Allocate()) Node(*this, F);
    1545             : }
    1546             : 
    1547         544 : void LazyCallGraph::updateGraphPtrs() {
    1548             :   // Walk the node map to update their graph pointers. While this iterates in
    1549             :   // an unstable order, the order has no effect so it remains correct.
    1550        2930 :   for (auto &FunctionNodePair : NodeMap)
    1551        1842 :     FunctionNodePair.second->G = this;
    1552             : 
    1553         544 :   for (auto *RC : PostOrderRefSCCs)
    1554           0 :     RC->G = this;
    1555         544 : }
    1556             : 
    1557             : template <typename RootsT, typename GetBeginT, typename GetEndT,
    1558             :           typename GetNodeT, typename FormSCCCallbackT>
    1559        1262 : void LazyCallGraph::buildGenericSCCs(RootsT &&Roots, GetBeginT &&GetBegin,
    1560             :                                      GetEndT &&GetEnd, GetNodeT &&GetNode,
    1561             :                                      FormSCCCallbackT &&FormSCC) {
    1562             :   using EdgeItT = decltype(GetBegin(std::declval<Node &>()));
    1563             : 
    1564             :   SmallVector<std::pair<Node *, EdgeItT>, 16> DFSStack;
    1565             :   SmallVector<Node *, 16> PendingSCCStack;
    1566             : 
    1567             :   // Scan down the stack and DFS across the call edges.
    1568        4530 :   for (Node *RootN : Roots) {
    1569             :     assert(DFSStack.empty() &&
    1570             :            "Cannot begin a new root with a non-empty DFS stack!");
    1571             :     assert(PendingSCCStack.empty() &&
    1572             :            "Cannot begin a new root with pending nodes for an SCC!");
    1573             : 
    1574             :     // Skip any nodes we've already reached in the DFS.
    1575        2225 :     if (RootN->DFSNumber != 0) {
    1576             :       assert(RootN->DFSNumber == -1 &&
    1577             :              "Shouldn't have any mid-DFS root nodes!");
    1578             :       continue;
    1579             :     }
    1580             : 
    1581        1706 :     RootN->DFSNumber = RootN->LowLink = 1;
    1582             :     int NextDFSNumber = 2;
    1583             : 
    1584        2396 :     DFSStack.push_back({RootN, GetBegin(*RootN)});
    1585             :     do {
    1586             :       Node *N;
    1587             :       EdgeItT I;
    1588             :       std::tie(N, I) = DFSStack.pop_back_val();
    1589             :       auto E = GetEnd(*N);
    1590        4771 :       while (I != E) {
    1591             :         Node &ChildN = GetNode(I);
    1592        3065 :         if (ChildN.DFSNumber == 0) {
    1593             :           // We haven't yet visited this child, so descend, pushing the current
    1594             :           // node onto the stack.
    1595         658 :           DFSStack.push_back({N, I});
    1596             : 
    1597         658 :           ChildN.DFSNumber = ChildN.LowLink = NextDFSNumber++;
    1598         658 :           N = &ChildN;
    1599         658 :           I = GetBegin(*N);
    1600         492 :           E = GetEnd(*N);
    1601             :           continue;
    1602             :         }
    1603             : 
    1604             :         // If the child has already been added to some child component, it
    1605             :         // couldn't impact the low-link of this parent because it isn't
    1606             :         // connected, and thus its low-link isn't relevant so skip it.
    1607        2809 :         if (ChildN.DFSNumber == -1) {
    1608         534 :           ++I;
    1609             :           continue;
    1610             :         }
    1611             : 
    1612             :         // Track the lowest linked child as the lowest link for this node.
    1613             :         assert(ChildN.LowLink > 0 && "Must have a positive low-link number!");
    1614         689 :         if (ChildN.LowLink < N->LowLink)
    1615         356 :           N->LowLink = ChildN.LowLink;
    1616             : 
    1617             :         // Move to the next edge.
    1618         257 :         ++I;
    1619             :       }
    1620             : 
    1621             :       // We've finished processing N and its descendants, put it on our pending
    1622             :       // SCC stack to eventually get merged into an SCC of nodes.
    1623        2364 :       PendingSCCStack.push_back(N);
    1624             : 
    1625             :       // If this node is linked to some lower entry, continue walking up the
    1626             :       // stack.
    1627        2364 :       if (N->LowLink != N->DFSNumber)
    1628         333 :         continue;
    1629             : 
    1630             :       // Otherwise, we've completed an SCC. Append it to our post order list of
    1631             :       // SCCs.
    1632             :       int RootDFSNumber = N->DFSNumber;
    1633             :       // Find the range of the node stack by walking down until we pass the
    1634             :       // root DFS number.
    1635        4062 :       auto SCCNodes = make_range(
    1636             :           PendingSCCStack.rbegin(),
    1637             :           find_if(reverse(PendingSCCStack), [RootDFSNumber](const Node *N) {
    1638             :             return N->DFSNumber < RootDFSNumber;
    1639             :           }));
    1640             :       // Form a new SCC out of these nodes and then clear them off our pending
    1641             :       // stack.
    1642        2031 :       FormSCC(SCCNodes);
    1643             :       PendingSCCStack.erase(SCCNodes.end().base(), PendingSCCStack.end());
    1644        2364 :     } while (!DFSStack.empty());
    1645             :   }
    1646        1262 : }
    1647             : 
    1648             : /// Build the internal SCCs for a RefSCC from a sequence of nodes.
    1649             : ///
    1650             : /// Appends the SCCs to the provided vector and updates the map with their
    1651             : /// indices. Both the vector and map must be empty when passed into this
    1652             : /// routine.
    1653         983 : void LazyCallGraph::buildSCCs(RefSCC &RC, node_stack_range Nodes) {
    1654             :   assert(RC.SCCs.empty() && "Already built SCCs!");
    1655             :   assert(RC.SCCIndices.empty() && "Already mapped SCC indices!");
    1656             : 
    1657        2165 :   for (Node *N : Nodes) {
    1658             :     assert(N->LowLink >= (*Nodes.begin())->LowLink &&
    1659             :            "We cannot have a low link in an SCC lower than its root on the "
    1660             :            "stack!");
    1661             : 
    1662             :     // This node will go into the next RefSCC, clear out its DFS and low link
    1663             :     // as we scan.
    1664        1182 :     N->DFSNumber = N->LowLink = 0;
    1665             :   }
    1666             : 
    1667             :   // Each RefSCC contains a DAG of the call SCCs. To build these, we do
    1668             :   // a direct walk of the call edges using Tarjan's algorithm. We reuse the
    1669             :   // internal storage as we won't need it for the outer graph's DFS any longer.
    1670         983 :   buildGenericSCCs(
    1671             :       Nodes, [](Node &N) { return N->call_begin(); },
    1672             :       [](Node &N) { return N->call_end(); },
    1673             :       [](EdgeSequence::call_iterator I) -> Node & { return I->getNode(); },
    1674        5508 :       [this, &RC](node_stack_range Nodes) {
    1675        2096 :         RC.SCCs.push_back(createSCC(RC, Nodes));
    1676        3278 :         for (Node &N : *RC.SCCs.back()) {
    1677        1182 :           N.DFSNumber = N.LowLink = -1;
    1678        3546 :           SCCMap[&N] = RC.SCCs.back();
    1679             :         }
    1680        1048 :       });
    1681             : 
    1682             :   // Wire up the SCC indices.
    1683        2031 :   for (int i = 0, Size = RC.SCCs.size(); i < Size; ++i)
    1684        3144 :     RC.SCCIndices[RC.SCCs[i]] = i;
    1685         983 : }
    1686             : 
    1687         521 : void LazyCallGraph::buildRefSCCs() {
    1688         521 :   if (EntryEdges.empty() || !PostOrderRefSCCs.empty())
    1689             :     // RefSCCs are either non-existent or already built!
    1690         242 :     return;
    1691             : 
    1692             :   assert(RefSCCIndices.empty() && "Already mapped RefSCC indices!");
    1693             : 
    1694             :   SmallVector<Node *, 16> Roots;
    1695        1322 :   for (Edge &E : *this)
    1696        1043 :     Roots.push_back(&E.getNode());
    1697             : 
    1698             :   // The roots will be popped of a stack, so use reverse to get a less
    1699             :   // surprising order. This doesn't change any of the semantics anywhere.
    1700             :   std::reverse(Roots.begin(), Roots.end());
    1701             : 
    1702         279 :   buildGenericSCCs(
    1703             :       Roots,
    1704        1182 :       [](Node &N) {
    1705             :         // We need to populate each node as we begin to walk its edges.
    1706             :         N.populate();
    1707        1182 :         return N->begin();
    1708             :       },
    1709             :       [](Node &N) { return N->end(); },
    1710             :       [](EdgeSequence::iterator I) -> Node & { return I->getNode(); },
    1711        3932 :       [this](node_stack_range Nodes) {
    1712         983 :         RefSCC *NewRC = createRefSCC(*this);
    1713         983 :         buildSCCs(*NewRC, Nodes);
    1714             : 
    1715             :         // Push the new node into the postorder list and remember its position
    1716             :         // in the index map.
    1717             :         bool Inserted =
    1718        1966 :             RefSCCIndices.insert({NewRC, PostOrderRefSCCs.size()}).second;
    1719             :         (void)Inserted;
    1720             :         assert(Inserted && "Cannot already have this RefSCC in the index map!");
    1721         983 :         PostOrderRefSCCs.push_back(NewRC);
    1722             : #ifndef NDEBUG
    1723             :         NewRC->verify();
    1724             : #endif
    1725         983 :       });
    1726             : }
    1727             : 
    1728             : AnalysisKey LazyCallGraphAnalysis::Key;
    1729             : 
    1730           2 : LazyCallGraphPrinterPass::LazyCallGraphPrinterPass(raw_ostream &OS) : OS(OS) {}
    1731             : 
    1732          33 : static void printNode(raw_ostream &OS, LazyCallGraph::Node &N) {
    1733          33 :   OS << "  Edges in function: " << N.getFunction().getName() << "\n";
    1734          74 :   for (LazyCallGraph::Edge &E : N.populate())
    1735          82 :     OS << "    " << (E.isCall() ? "call" : "ref ") << " -> "
    1736          41 :        << E.getFunction().getName() << "\n";
    1737             : 
    1738          33 :   OS << "\n";
    1739          33 : }
    1740             : 
    1741          25 : static void printSCC(raw_ostream &OS, LazyCallGraph::SCC &C) {
    1742             :   ptrdiff_t Size = size(C);
    1743          25 :   OS << "    SCC with " << Size << " functions:\n";
    1744             : 
    1745          55 :   for (LazyCallGraph::Node &N : C)
    1746          30 :     OS << "      " << N.getFunction().getName() << "\n";
    1747          25 : }
    1748             : 
    1749          22 : static void printRefSCC(raw_ostream &OS, LazyCallGraph::RefSCC &C) {
    1750             :   ptrdiff_t Size = size(C);
    1751          22 :   OS << "  RefSCC with " << Size << " call SCCs:\n";
    1752             : 
    1753          47 :   for (LazyCallGraph::SCC &InnerC : C)
    1754          25 :     printSCC(OS, InnerC);
    1755             : 
    1756          22 :   OS << "\n";
    1757          22 : }
    1758             : 
    1759           2 : PreservedAnalyses LazyCallGraphPrinterPass::run(Module &M,
    1760             :                                                 ModuleAnalysisManager &AM) {
    1761             :   LazyCallGraph &G = AM.getResult<LazyCallGraphAnalysis>(M);
    1762             : 
    1763           2 :   OS << "Printing the call graph for module: " << M.getModuleIdentifier()
    1764           2 :      << "\n\n";
    1765             : 
    1766          35 :   for (Function &F : M)
    1767          33 :     printNode(OS, G.get(F));
    1768             : 
    1769           2 :   G.buildRefSCCs();
    1770          46 :   for (LazyCallGraph::RefSCC &C : G.postorder_ref_sccs())
    1771          22 :     printRefSCC(OS, C);
    1772             : 
    1773           2 :   return PreservedAnalyses::all();
    1774             : }
    1775             : 
    1776           0 : LazyCallGraphDOTPrinterPass::LazyCallGraphDOTPrinterPass(raw_ostream &OS)
    1777           0 :     : OS(OS) {}
    1778             : 
    1779           0 : static void printNodeDOT(raw_ostream &OS, LazyCallGraph::Node &N) {
    1780           0 :   std::string Name = "\"" + DOT::EscapeString(N.getFunction().getName()) + "\"";
    1781             : 
    1782           0 :   for (LazyCallGraph::Edge &E : N.populate()) {
    1783           0 :     OS << "  " << Name << " -> \""
    1784           0 :        << DOT::EscapeString(E.getFunction().getName()) << "\"";
    1785           0 :     if (!E.isCall()) // It is a ref edge.
    1786           0 :       OS << " [style=dashed,label=\"ref\"]";
    1787           0 :     OS << ";\n";
    1788             :   }
    1789             : 
    1790           0 :   OS << "\n";
    1791           0 : }
    1792             : 
    1793           0 : PreservedAnalyses LazyCallGraphDOTPrinterPass::run(Module &M,
    1794             :                                                    ModuleAnalysisManager &AM) {
    1795             :   LazyCallGraph &G = AM.getResult<LazyCallGraphAnalysis>(M);
    1796             : 
    1797           0 :   OS << "digraph \"" << DOT::EscapeString(M.getModuleIdentifier()) << "\" {\n";
    1798             : 
    1799           0 :   for (Function &F : M)
    1800           0 :     printNodeDOT(OS, G.get(F));
    1801             : 
    1802           0 :   OS << "}\n";
    1803             : 
    1804           0 :   return PreservedAnalyses::all();
    1805             : }

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