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llvm/lib/Analysis/LazyCallGraph.cpp
Chandler Carruth cfe129ba52 [PM/LCG] Teach LCG to support spurious reference edges. 
Somewhat amazingly, this only requires teaching it to clean them up when
deleting a dead function from the graph. And we already have exactly the
necessary data structures to do that in the parent RefSCCs.

This allows ArgPromote to work in a much simpler way be merely letting
reference edges linger in the graph after the causing IR is deleted. We
will clean up these edges when we run any function pass over the IR, but
don't remove them eagerly.

This avoids all of the quadratic update issues both in the current pass
manager and in my previous attempt with the new pass manager.

Differential Revision: https://reviews.llvm.org/D29579

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@294663 91177308-0d34-0410-b5e6-96231b3b80d8
2017-02-09 23:30:14 +00:00

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//===- LazyCallGraph.cpp - Analysis of a Module's call graph --------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/LazyCallGraph.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/ADT/Sequence.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/InstVisitor.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/PassManager.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/GraphWriter.h"
#include <utility>
using namespace llvm;
#define DEBUG_TYPE "lcg"
void LazyCallGraph::EdgeSequence::insertEdgeInternal(Node &TargetN,
Edge::Kind EK) {
EdgeIndexMap.insert({&TargetN, Edges.size()});
Edges.emplace_back(TargetN, EK);
}
void LazyCallGraph::EdgeSequence::setEdgeKind(Node &TargetN, Edge::Kind EK) {
Edges[EdgeIndexMap.find(&TargetN)->second].setKind(EK);
}
bool LazyCallGraph::EdgeSequence::removeEdgeInternal(Node &TargetN) {
auto IndexMapI = EdgeIndexMap.find(&TargetN);
if (IndexMapI == EdgeIndexMap.end())
return false;
Edges[IndexMapI->second] = Edge();
EdgeIndexMap.erase(IndexMapI);
return true;
}
static void addEdge(SmallVectorImpl<LazyCallGraph::Edge> &Edges,
DenseMap<LazyCallGraph::Node *, int> &EdgeIndexMap,
LazyCallGraph::Node &N, LazyCallGraph::Edge::Kind EK) {
if (!EdgeIndexMap.insert({&N, Edges.size()}).second)
return;
DEBUG(dbgs() << " Added callable function: " << N.getName() << "\n");
Edges.emplace_back(LazyCallGraph::Edge(N, EK));
}
LazyCallGraph::EdgeSequence &LazyCallGraph::Node::populateSlow() {
assert(!Edges && "Must not have already populated the edges for this node!");
DEBUG(dbgs() << " Adding functions called by '" << getName()
<< "' to the graph.\n");
Edges = EdgeSequence();
SmallVector<Constant *, 16> Worklist;
SmallPtrSet<Function *, 4> Callees;
SmallPtrSet<Constant *, 16> Visited;
// Find all the potential call graph edges in this function. We track both
// actual call edges and indirect references to functions. The direct calls
// are trivially added, but to accumulate the latter we walk the instructions
// and add every operand which is a constant to the worklist to process
// afterward.
//
// Note that we consider *any* function with a definition to be a viable
// edge. Even if the function's definition is subject to replacement by
// some other module (say, a weak definition) there may still be
// optimizations which essentially speculate based on the definition and
// a way to check that the specific definition is in fact the one being
// used. For example, this could be done by moving the weak definition to
// a strong (internal) definition and making the weak definition be an
// alias. Then a test of the address of the weak function against the new
// strong definition's address would be an effective way to determine the
// safety of optimizing a direct call edge.
for (BasicBlock &BB : *F)
for (Instruction &I : BB) {
if (auto CS = CallSite(&I))
if (Function *Callee = CS.getCalledFunction())
if (!Callee->isDeclaration())
if (Callees.insert(Callee).second) {
Visited.insert(Callee);
addEdge(Edges->Edges, Edges->EdgeIndexMap, G->get(*Callee),
LazyCallGraph::Edge::Call);
}
for (Value *Op : I.operand_values())
if (Constant *C = dyn_cast<Constant>(Op))
if (Visited.insert(C).second)
Worklist.push_back(C);
}
// We've collected all the constant (and thus potentially function or
// function containing) operands to all of the instructions in the function.
// Process them (recursively) collecting every function found.
visitReferences(Worklist, Visited, [&](Function &F) {
addEdge(Edges->Edges, Edges->EdgeIndexMap, G->get(F),
LazyCallGraph::Edge::Ref);
});
return *Edges;
}
void LazyCallGraph::Node::replaceFunction(Function &NewF) {
assert(F != &NewF && "Must not replace a function with itself!");
F = &NewF;
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void LazyCallGraph::Node::dump() const {
dbgs() << *this << '\n';
}
#endif
LazyCallGraph::LazyCallGraph(Module &M) {
DEBUG(dbgs() << "Building CG for module: " << M.getModuleIdentifier()
<< "\n");
for (Function &F : M)
if (!F.isDeclaration() && !F.hasLocalLinkage()) {
DEBUG(dbgs() << " Adding '" << F.getName()
<< "' to entry set of the graph.\n");
addEdge(EntryEdges.Edges, EntryEdges.EdgeIndexMap, get(F), Edge::Ref);
}
// Now add entry nodes for functions reachable via initializers to globals.
SmallVector<Constant *, 16> Worklist;
SmallPtrSet<Constant *, 16> Visited;
for (GlobalVariable &GV : M.globals())
if (GV.hasInitializer())
if (Visited.insert(GV.getInitializer()).second)
Worklist.push_back(GV.getInitializer());
DEBUG(dbgs() << " Adding functions referenced by global initializers to the "
"entry set.\n");
visitReferences(Worklist, Visited, [&](Function &F) {
addEdge(EntryEdges.Edges, EntryEdges.EdgeIndexMap, get(F),
LazyCallGraph::Edge::Ref);
});
}
LazyCallGraph::LazyCallGraph(LazyCallGraph &&G)
: BPA(std::move(G.BPA)), NodeMap(std::move(G.NodeMap)),
EntryEdges(std::move(G.EntryEdges)), SCCBPA(std::move(G.SCCBPA)),
SCCMap(std::move(G.SCCMap)), LeafRefSCCs(std::move(G.LeafRefSCCs)) {
updateGraphPtrs();
}
LazyCallGraph &LazyCallGraph::operator=(LazyCallGraph &&G) {
BPA = std::move(G.BPA);
NodeMap = std::move(G.NodeMap);
EntryEdges = std::move(G.EntryEdges);
SCCBPA = std::move(G.SCCBPA);
SCCMap = std::move(G.SCCMap);
LeafRefSCCs = std::move(G.LeafRefSCCs);
updateGraphPtrs();
return *this;
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void LazyCallGraph::SCC::dump() const {
dbgs() << *this << '\n';
}
#endif
#ifndef NDEBUG
void LazyCallGraph::SCC::verify() {
assert(OuterRefSCC && "Can't have a null RefSCC!");
assert(!Nodes.empty() && "Can't have an empty SCC!");
for (Node *N : Nodes) {
assert(N && "Can't have a null node!");
assert(OuterRefSCC->G->lookupSCC(*N) == this &&
"Node does not map to this SCC!");
assert(N->DFSNumber == -1 &&
"Must set DFS numbers to -1 when adding a node to an SCC!");
assert(N->LowLink == -1 &&
"Must set low link to -1 when adding a node to an SCC!");
for (Edge &E : **N)
assert(E.getNode() && "Can't have an unpopulated node!");
}
}
#endif
bool LazyCallGraph::SCC::isParentOf(const SCC &C) const {
if (this == &C)
return false;
for (Node &N : *this)
for (Edge &E : N->calls())
if (OuterRefSCC->G->lookupSCC(E.getNode()) == &C)
return true;
// No edges found.
return false;
}
bool LazyCallGraph::SCC::isAncestorOf(const SCC &TargetC) const {
if (this == &TargetC)
return false;
LazyCallGraph &G = *OuterRefSCC->G;
// Start with this SCC.
SmallPtrSet<const SCC *, 16> Visited = {this};
SmallVector<const SCC *, 16> Worklist = {this};
// Walk down the graph until we run out of edges or find a path to TargetC.
do {
const SCC &C = *Worklist.pop_back_val();
for (Node &N : C)
for (Edge &E : N->calls()) {
SCC *CalleeC = G.lookupSCC(E.getNode());
if (!CalleeC)
continue;
// If the callee's SCC is the TargetC, we're done.
if (CalleeC == &TargetC)
return true;
// If this is the first time we've reached this SCC, put it on the
// worklist to recurse through.
if (Visited.insert(CalleeC).second)
Worklist.push_back(CalleeC);
}
} while (!Worklist.empty());
// No paths found.
return false;
}
LazyCallGraph::RefSCC::RefSCC(LazyCallGraph &G) : G(&G) {}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void LazyCallGraph::RefSCC::dump() const {
dbgs() << *this << '\n';
}
#endif
#ifndef NDEBUG
void LazyCallGraph::RefSCC::verify() {
assert(G && "Can't have a null graph!");
assert(!SCCs.empty() && "Can't have an empty SCC!");
// Verify basic properties of the SCCs.
SmallPtrSet<SCC *, 4> SCCSet;
for (SCC *C : SCCs) {
assert(C && "Can't have a null SCC!");
C->verify();
assert(&C->getOuterRefSCC() == this &&
"SCC doesn't think it is inside this RefSCC!");
bool Inserted = SCCSet.insert(C).second;
assert(Inserted && "Found a duplicate SCC!");
auto IndexIt = SCCIndices.find(C);
assert(IndexIt != SCCIndices.end() &&
"Found an SCC that doesn't have an index!");
}
// Check that our indices map correctly.
for (auto &SCCIndexPair : SCCIndices) {
SCC *C = SCCIndexPair.first;
int i = SCCIndexPair.second;
assert(C && "Can't have a null SCC in the indices!");
assert(SCCSet.count(C) && "Found an index for an SCC not in the RefSCC!");
assert(SCCs[i] == C && "Index doesn't point to SCC!");
}
// Check that the SCCs are in fact in post-order.
for (int i = 0, Size = SCCs.size(); i < Size; ++i) {
SCC &SourceSCC = *SCCs[i];
for (Node &N : SourceSCC)
for (Edge &E : *N) {
if (!E.isCall())
continue;
SCC &TargetSCC = *G->lookupSCC(E.getNode());
if (&TargetSCC.getOuterRefSCC() == this) {
assert(SCCIndices.find(&TargetSCC)->second <= i &&
"Edge between SCCs violates post-order relationship.");
continue;
}
assert(TargetSCC.getOuterRefSCC().Parents.count(this) &&
"Edge to a RefSCC missing us in its parent set.");
}
}
// Check that our parents are actually parents.
for (RefSCC *ParentRC : Parents) {
assert(ParentRC != this && "Cannot be our own parent!");
auto HasConnectingEdge = [&] {
for (SCC &C : *ParentRC)
for (Node &N : C)
for (Edge &E : *N)
if (G->lookupRefSCC(E.getNode()) == this)
return true;
return false;
};
assert(HasConnectingEdge() && "No edge connects the parent to us!");
}
}
#endif
bool LazyCallGraph::RefSCC::isDescendantOf(const RefSCC &C) const {
// Walk up the parents of this SCC and verify that we eventually find C.
SmallVector<const RefSCC *, 4> AncestorWorklist;
AncestorWorklist.push_back(this);
do {
const RefSCC *AncestorC = AncestorWorklist.pop_back_val();
if (AncestorC->isChildOf(C))
return true;
for (const RefSCC *ParentC : AncestorC->Parents)
AncestorWorklist.push_back(ParentC);
} while (!AncestorWorklist.empty());
return false;
}
/// Generic helper that updates a postorder sequence of SCCs for a potentially
/// cycle-introducing edge insertion.
///
/// A postorder sequence of SCCs of a directed graph has one fundamental
/// property: all deges in the DAG of SCCs point "up" the sequence. That is,
/// all edges in the SCC DAG point to prior SCCs in the sequence.
///
/// This routine both updates a postorder sequence and uses that sequence to
/// compute the set of SCCs connected into a cycle. It should only be called to
/// insert a "downward" edge which will require changing the sequence to
/// restore it to a postorder.
///
/// When inserting an edge from an earlier SCC to a later SCC in some postorder
/// sequence, all of the SCCs which may be impacted are in the closed range of
/// those two within the postorder sequence. The algorithm used here to restore
/// the state is as follows:
///
/// 1) Starting from the source SCC, construct a set of SCCs which reach the
/// source SCC consisting of just the source SCC. Then scan toward the
/// target SCC in postorder and for each SCC, if it has an edge to an SCC
/// in the set, add it to the set. Otherwise, the source SCC is not
/// a successor, move it in the postorder sequence to immediately before
/// the source SCC, shifting the source SCC and all SCCs in the set one
/// position toward the target SCC. Stop scanning after processing the
/// target SCC.
/// 2) If the source SCC is now past the target SCC in the postorder sequence,
/// and thus the new edge will flow toward the start, we are done.
/// 3) Otherwise, starting from the target SCC, walk all edges which reach an
/// SCC between the source and the target, and add them to the set of
/// connected SCCs, then recurse through them. Once a complete set of the
/// SCCs the target connects to is known, hoist the remaining SCCs between
/// the source and the target to be above the target. Note that there is no
/// need to process the source SCC, it is already known to connect.
/// 4) At this point, all of the SCCs in the closed range between the source
/// SCC and the target SCC in the postorder sequence are connected,
/// including the target SCC and the source SCC. Inserting the edge from
/// the source SCC to the target SCC will form a cycle out of precisely
/// these SCCs. Thus we can merge all of the SCCs in this closed range into
/// a single SCC.
///
/// This process has various important properties:
/// - Only mutates the SCCs when adding the edge actually changes the SCC
/// structure.
/// - Never mutates SCCs which are unaffected by the change.
/// - Updates the postorder sequence to correctly satisfy the postorder
/// constraint after the edge is inserted.
/// - Only reorders SCCs in the closed postorder sequence from the source to
/// the target, so easy to bound how much has changed even in the ordering.
/// - Big-O is the number of edges in the closed postorder range of SCCs from
/// source to target.
///
/// This helper routine, in addition to updating the postorder sequence itself
/// will also update a map from SCCs to indices within that sequecne.
///
/// The sequence and the map must operate on pointers to the SCC type.
///
/// Two callbacks must be provided. The first computes the subset of SCCs in
/// the postorder closed range from the source to the target which connect to
/// the source SCC via some (transitive) set of edges. The second computes the
/// subset of the same range which the target SCC connects to via some
/// (transitive) set of edges. Both callbacks should populate the set argument
/// provided.
template <typename SCCT, typename PostorderSequenceT, typename SCCIndexMapT,
typename ComputeSourceConnectedSetCallableT,
typename ComputeTargetConnectedSetCallableT>
static iterator_range<typename PostorderSequenceT::iterator>
updatePostorderSequenceForEdgeInsertion(
SCCT &SourceSCC, SCCT &TargetSCC, PostorderSequenceT &SCCs,
SCCIndexMapT &SCCIndices,
ComputeSourceConnectedSetCallableT ComputeSourceConnectedSet,
ComputeTargetConnectedSetCallableT ComputeTargetConnectedSet) {
int SourceIdx = SCCIndices[&SourceSCC];
int TargetIdx = SCCIndices[&TargetSCC];
assert(SourceIdx < TargetIdx && "Cannot have equal indices here!");
SmallPtrSet<SCCT *, 4> ConnectedSet;
// Compute the SCCs which (transitively) reach the source.
ComputeSourceConnectedSet(ConnectedSet);
// Partition the SCCs in this part of the port-order sequence so only SCCs
// connecting to the source remain between it and the target. This is
// a benign partition as it preserves postorder.
auto SourceI = std::stable_partition(
SCCs.begin() + SourceIdx, SCCs.begin() + TargetIdx + 1,
[&ConnectedSet](SCCT *C) { return !ConnectedSet.count(C); });
for (int i = SourceIdx, e = TargetIdx + 1; i < e; ++i)
SCCIndices.find(SCCs[i])->second = i;
// If the target doesn't connect to the source, then we've corrected the
// post-order and there are no cycles formed.
if (!ConnectedSet.count(&TargetSCC)) {
assert(SourceI > (SCCs.begin() + SourceIdx) &&
"Must have moved the source to fix the post-order.");
assert(*std::prev(SourceI) == &TargetSCC &&
"Last SCC to move should have bene the target.");
// Return an empty range at the target SCC indicating there is nothing to
// merge.
return make_range(std::prev(SourceI), std::prev(SourceI));
}
assert(SCCs[TargetIdx] == &TargetSCC &&
"Should not have moved target if connected!");
SourceIdx = SourceI - SCCs.begin();
assert(SCCs[SourceIdx] == &SourceSCC &&
"Bad updated index computation for the source SCC!");
// See whether there are any remaining intervening SCCs between the source
// and target. If so we need to make sure they all are reachable form the
// target.
if (SourceIdx + 1 < TargetIdx) {
ConnectedSet.clear();
ComputeTargetConnectedSet(ConnectedSet);
// Partition SCCs so that only SCCs reached from the target remain between
// the source and the target. This preserves postorder.
auto TargetI = std::stable_partition(
SCCs.begin() + SourceIdx + 1, SCCs.begin() + TargetIdx + 1,
[&ConnectedSet](SCCT *C) { return ConnectedSet.count(C); });
for (int i = SourceIdx + 1, e = TargetIdx + 1; i < e; ++i)
SCCIndices.find(SCCs[i])->second = i;
TargetIdx = std::prev(TargetI) - SCCs.begin();
assert(SCCs[TargetIdx] == &TargetSCC &&
"Should always end with the target!");
}
// At this point, we know that connecting source to target forms a cycle
// because target connects back to source, and we know that all of the SCCs
// between the source and target in the postorder sequence participate in that
// cycle.
return make_range(SCCs.begin() + SourceIdx, SCCs.begin() + TargetIdx);
}
SmallVector<LazyCallGraph::SCC *, 1>
LazyCallGraph::RefSCC::switchInternalEdgeToCall(Node &SourceN, Node &TargetN) {
assert(!(*SourceN)[TargetN].isCall() && "Must start with a ref edge!");
SmallVector<SCC *, 1> DeletedSCCs;
#ifndef NDEBUG
// In a debug build, verify the RefSCC is valid to start with and when this
// routine finishes.
verify();
auto VerifyOnExit = make_scope_exit([&]() { verify(); });
#endif
SCC &SourceSCC = *G->lookupSCC(SourceN);
SCC &TargetSCC = *G->lookupSCC(TargetN);
// If the two nodes are already part of the same SCC, we're also done as
// we've just added more connectivity.
if (&SourceSCC == &TargetSCC) {
SourceN->setEdgeKind(TargetN, Edge::Call);
return DeletedSCCs;
}
// At this point we leverage the postorder list of SCCs to detect when the
// insertion of an edge changes the SCC structure in any way.
//
// First and foremost, we can eliminate the need for any changes when the
// edge is toward the beginning of the postorder sequence because all edges
// flow in that direction already. Thus adding a new one cannot form a cycle.
int SourceIdx = SCCIndices[&SourceSCC];
int TargetIdx = SCCIndices[&TargetSCC];
if (TargetIdx < SourceIdx) {
SourceN->setEdgeKind(TargetN, Edge::Call);
return DeletedSCCs;
}
// Compute the SCCs which (transitively) reach the source.
auto ComputeSourceConnectedSet = [&](SmallPtrSetImpl<SCC *> &ConnectedSet) {
#ifndef NDEBUG
// Check that the RefSCC is still valid before computing this as the
// results will be nonsensical of we've broken its invariants.
verify();
#endif
ConnectedSet.insert(&SourceSCC);
auto IsConnected = [&](SCC &C) {
for (Node &N : C)
for (Edge &E : N->calls())
if (ConnectedSet.count(G->lookupSCC(E.getNode())))
return true;
return false;
};
for (SCC *C :
make_range(SCCs.begin() + SourceIdx + 1, SCCs.begin() + TargetIdx + 1))
if (IsConnected(*C))
ConnectedSet.insert(C);
};
// Use a normal worklist to find which SCCs the target connects to. We still
// bound the search based on the range in the postorder list we care about,
// but because this is forward connectivity we just "recurse" through the
// edges.
auto ComputeTargetConnectedSet = [&](SmallPtrSetImpl<SCC *> &ConnectedSet) {
#ifndef NDEBUG
// Check that the RefSCC is still valid before computing this as the
// results will be nonsensical of we've broken its invariants.
verify();
#endif
ConnectedSet.insert(&TargetSCC);
SmallVector<SCC *, 4> Worklist;
Worklist.push_back(&TargetSCC);
do {
SCC &C = *Worklist.pop_back_val();
for (Node &N : C)
for (Edge &E : *N) {
if (!E.isCall())
continue;
SCC &EdgeC = *G->lookupSCC(E.getNode());
if (&EdgeC.getOuterRefSCC() != this)
// Not in this RefSCC...
continue;
if (SCCIndices.find(&EdgeC)->second <= SourceIdx)
// Not in the postorder sequence between source and target.
continue;
if (ConnectedSet.insert(&EdgeC).second)
Worklist.push_back(&EdgeC);
}
} while (!Worklist.empty());
};
// Use a generic helper to update the postorder sequence of SCCs and return
// a range of any SCCs connected into a cycle by inserting this edge. This
// routine will also take care of updating the indices into the postorder
// sequence.
auto MergeRange = updatePostorderSequenceForEdgeInsertion(
SourceSCC, TargetSCC, SCCs, SCCIndices, ComputeSourceConnectedSet,
ComputeTargetConnectedSet);
// If the merge range is empty, then adding the edge didn't actually form any
// new cycles. We're done.
if (MergeRange.begin() == MergeRange.end()) {
// Now that the SCC structure is finalized, flip the kind to call.
SourceN->setEdgeKind(TargetN, Edge::Call);
return DeletedSCCs;
}
#ifndef NDEBUG
// Before merging, check that the RefSCC remains valid after all the
// postorder updates.
verify();
#endif
// Otherwise we need to merge all of the SCCs in the cycle into a single
// result SCC.
//
// NB: We merge into the target because all of these functions were already
// reachable from the target, meaning any SCC-wide properties deduced about it
// other than the set of functions within it will not have changed.
for (SCC *C : MergeRange) {
assert(C != &TargetSCC &&
"We merge *into* the target and shouldn't process it here!");
SCCIndices.erase(C);
TargetSCC.Nodes.append(C->Nodes.begin(), C->Nodes.end());
for (Node *N : C->Nodes)
G->SCCMap[N] = &TargetSCC;
C->clear();
DeletedSCCs.push_back(C);
}
// Erase the merged SCCs from the list and update the indices of the
// remaining SCCs.
int IndexOffset = MergeRange.end() - MergeRange.begin();
auto EraseEnd = SCCs.erase(MergeRange.begin(), MergeRange.end());
for (SCC *C : make_range(EraseEnd, SCCs.end()))
SCCIndices[C] -= IndexOffset;
// Now that the SCC structure is finalized, flip the kind to call.
SourceN->setEdgeKind(TargetN, Edge::Call);
// And we're done!
return DeletedSCCs;
}
void LazyCallGraph::RefSCC::switchTrivialInternalEdgeToRef(Node &SourceN,
Node &TargetN) {
assert((*SourceN)[TargetN].isCall() && "Must start with a call edge!");
#ifndef NDEBUG
// In a debug build, verify the RefSCC is valid to start with and when this
// routine finishes.
verify();
auto VerifyOnExit = make_scope_exit([&]() { verify(); });
#endif
assert(G->lookupRefSCC(SourceN) == this &&
"Source must be in this RefSCC.");
assert(G->lookupRefSCC(TargetN) == this &&
"Target must be in this RefSCC.");
assert(G->lookupSCC(SourceN) != G->lookupSCC(TargetN) &&
"Source and Target must be in separate SCCs for this to be trivial!");
// Set the edge kind.
SourceN->setEdgeKind(TargetN, Edge::Ref);
}
iterator_range<LazyCallGraph::RefSCC::iterator>
LazyCallGraph::RefSCC::switchInternalEdgeToRef(Node &SourceN, Node &TargetN) {
assert((*SourceN)[TargetN].isCall() && "Must start with a call edge!");
#ifndef NDEBUG
// In a debug build, verify the RefSCC is valid to start with and when this
// routine finishes.
verify();
auto VerifyOnExit = make_scope_exit([&]() { verify(); });
#endif
assert(G->lookupRefSCC(SourceN) == this &&
"Source must be in this RefSCC.");
assert(G->lookupRefSCC(TargetN) == this &&
"Target must be in this RefSCC.");
SCC &TargetSCC = *G->lookupSCC(TargetN);
assert(G->lookupSCC(SourceN) == &TargetSCC && "Source and Target must be in "
"the same SCC to require the "
"full CG update.");
// Set the edge kind.
SourceN->setEdgeKind(TargetN, Edge::Ref);
// Otherwise we are removing a call edge from a single SCC. This may break
// the cycle. In order to compute the new set of SCCs, we need to do a small
// DFS over the nodes within the SCC to form any sub-cycles that remain as
// distinct SCCs and compute a postorder over the resulting SCCs.
//
// However, we specially handle the target node. The target node is known to
// reach all other nodes in the original SCC by definition. This means that
// we want the old SCC to be replaced with an SCC contaning that node as it
// will be the root of whatever SCC DAG results from the DFS. Assumptions
// about an SCC such as the set of functions called will continue to hold,
// etc.
SCC &OldSCC = TargetSCC;
SmallVector<std::pair<Node *, EdgeSequence::call_iterator>, 16> DFSStack;
SmallVector<Node *, 16> PendingSCCStack;
SmallVector<SCC *, 4> NewSCCs;
// Prepare the nodes for a fresh DFS.
SmallVector<Node *, 16> Worklist;
Worklist.swap(OldSCC.Nodes);
for (Node *N : Worklist) {
N->DFSNumber = N->LowLink = 0;
G->SCCMap.erase(N);
}
// Force the target node to be in the old SCC. This also enables us to take
// a very significant short-cut in the standard Tarjan walk to re-form SCCs
// below: whenever we build an edge that reaches the target node, we know
// that the target node eventually connects back to all other nodes in our
// walk. As a consequence, we can detect and handle participants in that
// cycle without walking all the edges that form this connection, and instead
// by relying on the fundamental guarantee coming into this operation (all
// nodes are reachable from the target due to previously forming an SCC).
TargetN.DFSNumber = TargetN.LowLink = -1;
OldSCC.Nodes.push_back(&TargetN);
G->SCCMap[&TargetN] = &OldSCC;
// Scan down the stack and DFS across the call edges.
for (Node *RootN : Worklist) {
assert(DFSStack.empty() &&
"Cannot begin a new root with a non-empty DFS stack!");
assert(PendingSCCStack.empty() &&
"Cannot begin a new root with pending nodes for an SCC!");
// Skip any nodes we've already reached in the DFS.
if (RootN->DFSNumber != 0) {
assert(RootN->DFSNumber == -1 &&
"Shouldn't have any mid-DFS root nodes!");
continue;
}
RootN->DFSNumber = RootN->LowLink = 1;
int NextDFSNumber = 2;
DFSStack.push_back({RootN, (*RootN)->call_begin()});
do {
Node *N;
EdgeSequence::call_iterator I;
std::tie(N, I) = DFSStack.pop_back_val();
auto E = (*N)->call_end();
while (I != E) {
Node &ChildN = I->getNode();
if (ChildN.DFSNumber == 0) {
// We haven't yet visited this child, so descend, pushing the current
// node onto the stack.
DFSStack.push_back({N, I});
assert(!G->SCCMap.count(&ChildN) &&
"Found a node with 0 DFS number but already in an SCC!");
ChildN.DFSNumber = ChildN.LowLink = NextDFSNumber++;
N = &ChildN;
I = (*N)->call_begin();
E = (*N)->call_end();
continue;
}
// Check for the child already being part of some component.
if (ChildN.DFSNumber == -1) {
if (G->lookupSCC(ChildN) == &OldSCC) {
// If the child is part of the old SCC, we know that it can reach
// every other node, so we have formed a cycle. Pull the entire DFS
// and pending stacks into it. See the comment above about setting
// up the old SCC for why we do this.
int OldSize = OldSCC.size();
OldSCC.Nodes.push_back(N);
OldSCC.Nodes.append(PendingSCCStack.begin(), PendingSCCStack.end());
PendingSCCStack.clear();
while (!DFSStack.empty())
OldSCC.Nodes.push_back(DFSStack.pop_back_val().first);
for (Node &N : make_range(OldSCC.begin() + OldSize, OldSCC.end())) {
N.DFSNumber = N.LowLink = -1;
G->SCCMap[&N] = &OldSCC;
}
N = nullptr;
break;
}
// If the child has already been added to some child component, it
// couldn't impact the low-link of this parent because it isn't
// connected, and thus its low-link isn't relevant so skip it.
++I;
continue;
}
// Track the lowest linked child as the lowest link for this node.
assert(ChildN.LowLink > 0 && "Must have a positive low-link number!");
if (ChildN.LowLink < N->LowLink)
N->LowLink = ChildN.LowLink;
// Move to the next edge.
++I;
}
if (!N)
// Cleared the DFS early, start another round.
break;
// We've finished processing N and its descendents, put it on our pending
// SCC stack to eventually get merged into an SCC of nodes.
PendingSCCStack.push_back(N);
// If this node is linked to some lower entry, continue walking up the
// stack.
if (N->LowLink != N->DFSNumber)
continue;
// Otherwise, we've completed an SCC. Append it to our post order list of
// SCCs.
int RootDFSNumber = N->DFSNumber;
// Find the range of the node stack by walking down until we pass the
// root DFS number.
auto SCCNodes = make_range(
PendingSCCStack.rbegin(),
find_if(reverse(PendingSCCStack), [RootDFSNumber](const Node *N) {
return N->DFSNumber < RootDFSNumber;
}));
// Form a new SCC out of these nodes and then clear them off our pending
// stack.
NewSCCs.push_back(G->createSCC(*this, SCCNodes));
for (Node &N : *NewSCCs.back()) {
N.DFSNumber = N.LowLink = -1;
G->SCCMap[&N] = NewSCCs.back();
}
PendingSCCStack.erase(SCCNodes.end().base(), PendingSCCStack.end());
} while (!DFSStack.empty());
}
// Insert the remaining SCCs before the old one. The old SCC can reach all
// other SCCs we form because it contains the target node of the removed edge
// of the old SCC. This means that we will have edges into all of the new
// SCCs, which means the old one must come last for postorder.
int OldIdx = SCCIndices[&OldSCC];
SCCs.insert(SCCs.begin() + OldIdx, NewSCCs.begin(), NewSCCs.end());
// Update the mapping from SCC* to index to use the new SCC*s, and remove the
// old SCC from the mapping.
for (int Idx = OldIdx, Size = SCCs.size(); Idx < Size; ++Idx)
SCCIndices[SCCs[Idx]] = Idx;
return make_range(SCCs.begin() + OldIdx,
SCCs.begin() + OldIdx + NewSCCs.size());
}
void LazyCallGraph::RefSCC::switchOutgoingEdgeToCall(Node &SourceN,
Node &TargetN) {
assert(!(*SourceN)[TargetN].isCall() && "Must start with a ref edge!");
assert(G->lookupRefSCC(SourceN) == this && "Source must be in this RefSCC.");
assert(G->lookupRefSCC(TargetN) != this &&
"Target must not be in this RefSCC.");
#ifdef EXPENSIVE_CEHCKS
assert(G->lookupRefSCC(TargetN)->isDescendantOf(*this) &&
"Target must be a descendant of the Source.");
#endif
// Edges between RefSCCs are the same regardless of call or ref, so we can
// just flip the edge here.
SourceN->setEdgeKind(TargetN, Edge::Call);
#ifndef NDEBUG
// Check that the RefSCC is still valid.
verify();
#endif
}
void LazyCallGraph::RefSCC::switchOutgoingEdgeToRef(Node &SourceN,
Node &TargetN) {
assert((*SourceN)[TargetN].isCall() && "Must start with a call edge!");
assert(G->lookupRefSCC(SourceN) == this && "Source must be in this RefSCC.");
assert(G->lookupRefSCC(TargetN) != this &&
"Target must not be in this RefSCC.");
#ifdef EXPENSIVE_CEHCKS
assert(G->lookupRefSCC(TargetN)->isDescendantOf(*this) &&
"Target must be a descendant of the Source.");
#endif
// Edges between RefSCCs are the same regardless of call or ref, so we can
// just flip the edge here.
SourceN->setEdgeKind(TargetN, Edge::Ref);
#ifndef NDEBUG
// Check that the RefSCC is still valid.
verify();
#endif
}
void LazyCallGraph::RefSCC::insertInternalRefEdge(Node &SourceN,
Node &TargetN) {
assert(G->lookupRefSCC(SourceN) == this && "Source must be in this RefSCC.");
assert(G->lookupRefSCC(TargetN) == this && "Target must be in this RefSCC.");
SourceN->insertEdgeInternal(TargetN, Edge::Ref);
#ifndef NDEBUG
// Check that the RefSCC is still valid.
verify();
#endif
}
void LazyCallGraph::RefSCC::insertOutgoingEdge(Node &SourceN, Node &TargetN,
Edge::Kind EK) {
// First insert it into the caller.
SourceN->insertEdgeInternal(TargetN, EK);
assert(G->lookupRefSCC(SourceN) == this && "Source must be in this RefSCC.");
RefSCC &TargetC = *G->lookupRefSCC(TargetN);
assert(&TargetC != this && "Target must not be in this RefSCC.");
#ifdef EXPENSIVE_CEHCKS
assert(TargetC.isDescendantOf(*this) &&
"Target must be a descendant of the Source.");
#endif
// The only change required is to add this SCC to the parent set of the
// callee.
TargetC.Parents.insert(this);
#ifndef NDEBUG
// Check that the RefSCC is still valid.
verify();
#endif
}
SmallVector<LazyCallGraph::RefSCC *, 1>
LazyCallGraph::RefSCC::insertIncomingRefEdge(Node &SourceN, Node &TargetN) {
assert(G->lookupRefSCC(TargetN) == this && "Target must be in this RefSCC.");
RefSCC &SourceC = *G->lookupRefSCC(SourceN);
assert(&SourceC != this && "Source must not be in this RefSCC.");
#ifdef EXPENSIVE_CEHCKS
assert(SourceC.isDescendantOf(*this) &&
"Source must be a descendant of the Target.");
#endif
SmallVector<RefSCC *, 1> DeletedRefSCCs;
#ifndef NDEBUG
// In a debug build, verify the RefSCC is valid to start with and when this
// routine finishes.
verify();
auto VerifyOnExit = make_scope_exit([&]() { verify(); });
#endif
int SourceIdx = G->RefSCCIndices[&SourceC];
int TargetIdx = G->RefSCCIndices[this];
assert(SourceIdx < TargetIdx &&
"Postorder list doesn't see edge as incoming!");
// Compute the RefSCCs which (transitively) reach the source. We do this by
// working backwards from the source using the parent set in each RefSCC,
// skipping any RefSCCs that don't fall in the postorder range. This has the
// advantage of walking the sparser parent edge (in high fan-out graphs) but
// more importantly this removes examining all forward edges in all RefSCCs
// within the postorder range which aren't in fact connected. Only connected
// RefSCCs (and their edges) are visited here.
auto ComputeSourceConnectedSet = [&](SmallPtrSetImpl<RefSCC *> &Set) {
Set.insert(&SourceC);
SmallVector<RefSCC *, 4> Worklist;
Worklist.push_back(&SourceC);
do {
RefSCC &RC = *Worklist.pop_back_val();
for (RefSCC &ParentRC : RC.parents()) {
// Skip any RefSCCs outside the range of source to target in the
// postorder sequence.
int ParentIdx = G->getRefSCCIndex(ParentRC);
assert(ParentIdx > SourceIdx && "Parent cannot precede source in postorder!");
if (ParentIdx > TargetIdx)
continue;
if (Set.insert(&ParentRC).second)
// First edge connecting to this parent, add it to our worklist.
Worklist.push_back(&ParentRC);
}
} while (!Worklist.empty());
};
// Use a normal worklist to find which SCCs the target connects to. We still
// bound the search based on the range in the postorder list we care about,
// but because this is forward connectivity we just "recurse" through the
// edges.
auto ComputeTargetConnectedSet = [&](SmallPtrSetImpl<RefSCC *> &Set) {
Set.insert(this);
SmallVector<RefSCC *, 4> Worklist;
Worklist.push_back(this);
do {
RefSCC &RC = *Worklist.pop_back_val();
for (SCC &C : RC)
for (Node &N : C)
for (Edge &E : *N) {
RefSCC &EdgeRC = *G->lookupRefSCC(E.getNode());
if (G->getRefSCCIndex(EdgeRC) <= SourceIdx)
// Not in the postorder sequence between source and target.
continue;
if (Set.insert(&EdgeRC).second)
Worklist.push_back(&EdgeRC);
}
} while (!Worklist.empty());
};
// Use a generic helper to update the postorder sequence of RefSCCs and return
// a range of any RefSCCs connected into a cycle by inserting this edge. This
// routine will also take care of updating the indices into the postorder
// sequence.
iterator_range<SmallVectorImpl<RefSCC *>::iterator> MergeRange =
updatePostorderSequenceForEdgeInsertion(
SourceC, *this, G->PostOrderRefSCCs, G->RefSCCIndices,
ComputeSourceConnectedSet, ComputeTargetConnectedSet);
// Build a set so we can do fast tests for whether a RefSCC will end up as
// part of the merged RefSCC.
SmallPtrSet<RefSCC *, 16> MergeSet(MergeRange.begin(), MergeRange.end());
// This RefSCC will always be part of that set, so just insert it here.
MergeSet.insert(this);
// Now that we have identified all of the SCCs which need to be merged into
// a connected set with the inserted edge, merge all of them into this SCC.
SmallVector<SCC *, 16> MergedSCCs;
int SCCIndex = 0;
for (RefSCC *RC : MergeRange) {
assert(RC != this && "We're merging into the target RefSCC, so it "
"shouldn't be in the range.");
// Merge the parents which aren't part of the merge into the our parents.
for (RefSCC *ParentRC : RC->Parents)
if (!MergeSet.count(ParentRC))
Parents.insert(ParentRC);
RC->Parents.clear();
// Walk the inner SCCs to update their up-pointer and walk all the edges to
// update any parent sets.
// FIXME: We should try to find a way to avoid this (rather expensive) edge
// walk by updating the parent sets in some other manner.
for (SCC &InnerC : *RC) {
InnerC.OuterRefSCC = this;
SCCIndices[&InnerC] = SCCIndex++;
for (Node &N : InnerC) {
G->SCCMap[&N] = &InnerC;
for (Edge &E : *N) {
RefSCC &ChildRC = *G->lookupRefSCC(E.getNode());
if (MergeSet.count(&ChildRC))
continue;
ChildRC.Parents.erase(RC);
ChildRC.Parents.insert(this);
}
}
}
// Now merge in the SCCs. We can actually move here so try to reuse storage
// the first time through.
if (MergedSCCs.empty())
MergedSCCs = std::move(RC->SCCs);
else
MergedSCCs.append(RC->SCCs.begin(), RC->SCCs.end());
RC->SCCs.clear();
DeletedRefSCCs.push_back(RC);
}
// Append our original SCCs to the merged list and move it into place.
for (SCC &InnerC : *this)
SCCIndices[&InnerC] = SCCIndex++;
MergedSCCs.append(SCCs.begin(), SCCs.end());
SCCs = std::move(MergedSCCs);
// Remove the merged away RefSCCs from the post order sequence.
for (RefSCC *RC : MergeRange)
G->RefSCCIndices.erase(RC);
int IndexOffset = MergeRange.end() - MergeRange.begin();
auto EraseEnd =
G->PostOrderRefSCCs.erase(MergeRange.begin(), MergeRange.end());
for (RefSCC *RC : make_range(EraseEnd, G->PostOrderRefSCCs.end()))
G->RefSCCIndices[RC] -= IndexOffset;
// At this point we have a merged RefSCC with a post-order SCCs list, just
// connect the nodes to form the new edge.
SourceN->insertEdgeInternal(TargetN, Edge::Ref);
// We return the list of SCCs which were merged so that callers can
// invalidate any data they have associated with those SCCs. Note that these
// SCCs are no longer in an interesting state (they are totally empty) but
// the pointers will remain stable for the life of the graph itself.
return DeletedRefSCCs;
}
void LazyCallGraph::RefSCC::removeOutgoingEdge(Node &SourceN, Node &TargetN) {
assert(G->lookupRefSCC(SourceN) == this &&
"The source must be a member of this RefSCC.");
RefSCC &TargetRC = *G->lookupRefSCC(TargetN);
assert(&TargetRC != this && "The target must not be a member of this RefSCC");
assert(!is_contained(G->LeafRefSCCs, this) &&
"Cannot have a leaf RefSCC source.");
#ifndef NDEBUG
// In a debug build, verify the RefSCC is valid to start with and when this
// routine finishes.
verify();
auto VerifyOnExit = make_scope_exit([&]() { verify(); });
#endif
// First remove it from the node.
bool Removed = SourceN->removeEdgeInternal(TargetN);
(void)Removed;
assert(Removed && "Target not in the edge set for this caller?");
bool HasOtherEdgeToChildRC = false;
bool HasOtherChildRC = false;
for (SCC *InnerC : SCCs) {
for (Node &N : *InnerC) {
for (Edge &E : *N) {
RefSCC &OtherChildRC = *G->lookupRefSCC(E.getNode());
if (&OtherChildRC == &TargetRC) {
HasOtherEdgeToChildRC = true;
break;
}
if (&OtherChildRC != this)
HasOtherChildRC = true;
}
if (HasOtherEdgeToChildRC)
break;
}
if (HasOtherEdgeToChildRC)
break;
}
// Because the SCCs form a DAG, deleting such an edge cannot change the set
// of SCCs in the graph. However, it may cut an edge of the SCC DAG, making
// the source SCC no longer connected to the target SCC. If so, we need to
// update the target SCC's map of its parents.
if (!HasOtherEdgeToChildRC) {
bool Removed = TargetRC.Parents.erase(this);
(void)Removed;
assert(Removed &&
"Did not find the source SCC in the target SCC's parent list!");
// It may orphan an SCC if it is the last edge reaching it, but that does
// not violate any invariants of the graph.
if (TargetRC.Parents.empty())
DEBUG(dbgs() << "LCG: Update removing " << SourceN.getFunction().getName()
<< " -> " << TargetN.getFunction().getName()
<< " edge orphaned the callee's SCC!\n");
// It may make the Source SCC a leaf SCC.
if (!HasOtherChildRC)
G->LeafRefSCCs.push_back(this);
}
}
SmallVector<LazyCallGraph::RefSCC *, 1>
LazyCallGraph::RefSCC::removeInternalRefEdge(Node &SourceN, Node &TargetN) {
assert(!(*SourceN)[TargetN].isCall() &&
"Cannot remove a call edge, it must first be made a ref edge");
#ifndef NDEBUG
// In a debug build, verify the RefSCC is valid to start with and when this
// routine finishes.
verify();
auto VerifyOnExit = make_scope_exit([&]() { verify(); });
#endif
// First remove the actual edge.
bool Removed = SourceN->removeEdgeInternal(TargetN);
(void)Removed;
assert(Removed && "Target not in the edge set for this caller?");
// We return a list of the resulting *new* RefSCCs in post-order.
SmallVector<RefSCC *, 1> Result;
// Direct recursion doesn't impact the SCC graph at all.
if (&SourceN == &TargetN)
return Result;
// If this ref edge is within an SCC then there are sufficient other edges to
// form a cycle without this edge so removing it is a no-op.
SCC &SourceC = *G->lookupSCC(SourceN);
SCC &TargetC = *G->lookupSCC(TargetN);
if (&SourceC == &TargetC)
return Result;
// We build somewhat synthetic new RefSCCs by providing a postorder mapping
// for each inner SCC. We also store these associated with *nodes* rather
// than SCCs because this saves a round-trip through the node->SCC map and in
// the common case, SCCs are small. We will verify that we always give the
// same number to every node in the SCC such that these are equivalent.
const int RootPostOrderNumber = 0;
int PostOrderNumber = RootPostOrderNumber + 1;
SmallDenseMap<Node *, int> PostOrderMapping;
// Every node in the target SCC can already reach every node in this RefSCC
// (by definition). It is the only node we know will stay inside this RefSCC.
// Everything which transitively reaches Target will also remain in the
// RefSCC. We handle this by pre-marking that the nodes in the target SCC map
// back to the root post order number.
//
// This also enables us to take a very significant short-cut in the standard
// Tarjan walk to re-form RefSCCs below: whenever we build an edge that
// references the target node, we know that the target node eventually
// references all other nodes in our walk. As a consequence, we can detect
// and handle participants in that cycle without walking all the edges that
// form the connections, and instead by relying on the fundamental guarantee
// coming into this operation.
for (Node &N : TargetC)
PostOrderMapping[&N] = RootPostOrderNumber;
// Reset all the other nodes to prepare for a DFS over them, and add them to
// our worklist.
SmallVector<Node *, 8> Worklist;
for (SCC *C : SCCs) {
if (C == &TargetC)
continue;
for (Node &N : *C)
N.DFSNumber = N.LowLink = 0;
Worklist.append(C->Nodes.begin(), C->Nodes.end());
}
auto MarkNodeForSCCNumber = [&PostOrderMapping](Node &N, int Number) {
N.DFSNumber = N.LowLink = -1;
PostOrderMapping[&N] = Number;
};
SmallVector<std::pair<Node *, EdgeSequence::iterator>, 4> DFSStack;
SmallVector<Node *, 4> PendingRefSCCStack;
do {
assert(DFSStack.empty() &&
"Cannot begin a new root with a non-empty DFS stack!");
assert(PendingRefSCCStack.empty() &&
"Cannot begin a new root with pending nodes for an SCC!");
Node *RootN = Worklist.pop_back_val();
// Skip any nodes we've already reached in the DFS.
if (RootN->DFSNumber != 0) {
assert(RootN->DFSNumber == -1 &&
"Shouldn't have any mid-DFS root nodes!");
continue;
}
RootN->DFSNumber = RootN->LowLink = 1;
int NextDFSNumber = 2;
DFSStack.push_back({RootN, (*RootN)->begin()});
do {
Node *N;
EdgeSequence::iterator I;
std::tie(N, I) = DFSStack.pop_back_val();
auto E = (*N)->end();
assert(N->DFSNumber != 0 && "We should always assign a DFS number "
"before processing a node.");
while (I != E) {
Node &ChildN = I->getNode();
if (ChildN.DFSNumber == 0) {
// Mark that we should start at this child when next this node is the
// top of the stack. We don't start at the next child to ensure this
// child's lowlink is reflected.
DFSStack.push_back({N, I});
// Continue, resetting to the child node.
ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
N = &ChildN;
I = ChildN->begin();
E = ChildN->end();
continue;
}
if (ChildN.DFSNumber == -1) {
// Check if this edge's target node connects to the deleted edge's
// target node. If so, we know that every node connected will end up
// in this RefSCC, so collapse the entire current stack into the root
// slot in our SCC numbering. See above for the motivation of
// optimizing the target connected nodes in this way.
auto PostOrderI = PostOrderMapping.find(&ChildN);
if (PostOrderI != PostOrderMapping.end() &&
PostOrderI->second == RootPostOrderNumber) {
MarkNodeForSCCNumber(*N, RootPostOrderNumber);
while (!PendingRefSCCStack.empty())
MarkNodeForSCCNumber(*PendingRefSCCStack.pop_back_val(),
RootPostOrderNumber);
while (!DFSStack.empty())
MarkNodeForSCCNumber(*DFSStack.pop_back_val().first,
RootPostOrderNumber);
// Ensure we break all the way out of the enclosing loop.
N = nullptr;
break;
}
// If this child isn't currently in this RefSCC, no need to process
// it. However, we do need to remove this RefSCC from its RefSCC's
// parent set.
RefSCC &ChildRC = *G->lookupRefSCC(ChildN);
ChildRC.Parents.erase(this);
++I;
continue;
}
// Track the lowest link of the children, if any are still in the stack.
// Any child not on the stack will have a LowLink of -1.
assert(ChildN.LowLink != 0 &&
"Low-link must not be zero with a non-zero DFS number.");
if (ChildN.LowLink >= 0 && ChildN.LowLink < N->LowLink)
N->LowLink = ChildN.LowLink;
++I;
}
if (!N)
// We short-circuited this node.
break;
// We've finished processing N and its descendents, put it on our pending
// stack to eventually get merged into a RefSCC.
PendingRefSCCStack.push_back(N);
// If this node is linked to some lower entry, continue walking up the
// stack.
if (N->LowLink != N->DFSNumber) {
assert(!DFSStack.empty() &&
"We never found a viable root for a RefSCC to pop off!");
continue;
}
// Otherwise, form a new RefSCC from the top of the pending node stack.
int RootDFSNumber = N->DFSNumber;
// Find the range of the node stack by walking down until we pass the
// root DFS number.
auto RefSCCNodes = make_range(
PendingRefSCCStack.rbegin(),
find_if(reverse(PendingRefSCCStack), [RootDFSNumber](const Node *N) {
return N->DFSNumber < RootDFSNumber;
}));
// Mark the postorder number for these nodes and clear them off the
// stack. We'll use the postorder number to pull them into RefSCCs at the
// end. FIXME: Fuse with the loop above.
int RefSCCNumber = PostOrderNumber++;
for (Node *N : RefSCCNodes)
MarkNodeForSCCNumber(*N, RefSCCNumber);
PendingRefSCCStack.erase(RefSCCNodes.end().base(),
PendingRefSCCStack.end());
} while (!DFSStack.empty());
assert(DFSStack.empty() && "Didn't flush the entire DFS stack!");
assert(PendingRefSCCStack.empty() && "Didn't flush all pending nodes!");
} while (!Worklist.empty());
// We now have a post-order numbering for RefSCCs and a mapping from each
// node in this RefSCC to its final RefSCC. We create each new RefSCC node
// (re-using this RefSCC node for the root) and build a radix-sort style map
// from postorder number to the RefSCC. We then append SCCs to each of these
// RefSCCs in the order they occured in the original SCCs container.
for (int i = 1; i < PostOrderNumber; ++i)
Result.push_back(G->createRefSCC(*G));
// Insert the resulting postorder sequence into the global graph postorder
// sequence before the current RefSCC in that sequence. The idea being that
// this RefSCC is the target of the reference edge removed, and thus has
// a direct or indirect edge to every other RefSCC formed and so must be at
// the end of any postorder traversal.
//
// FIXME: It'd be nice to change the APIs so that we returned an iterator
// range over the global postorder sequence and generally use that sequence
// rather than building a separate result vector here.
if (!Result.empty()) {
int Idx = G->getRefSCCIndex(*this);
G->PostOrderRefSCCs.insert(G->PostOrderRefSCCs.begin() + Idx,
Result.begin(), Result.end());
for (int i : seq<int>(Idx, G->PostOrderRefSCCs.size()))
G->RefSCCIndices[G->PostOrderRefSCCs[i]] = i;
assert(G->PostOrderRefSCCs[G->getRefSCCIndex(*this)] == this &&
"Failed to update this RefSCC's index after insertion!");
}
for (SCC *C : SCCs) {
auto PostOrderI = PostOrderMapping.find(&*C->begin());
assert(PostOrderI != PostOrderMapping.end() &&
"Cannot have missing mappings for nodes!");
int SCCNumber = PostOrderI->second;
#ifndef NDEBUG
for (Node &N : *C)
assert(PostOrderMapping.find(&N)->second == SCCNumber &&
"Cannot have different numbers for nodes in the same SCC!");
#endif
if (SCCNumber == 0)
// The root node is handled separately by removing the SCCs.
continue;
RefSCC &RC = *Result[SCCNumber - 1];
int SCCIndex = RC.SCCs.size();
RC.SCCs.push_back(C);
RC.SCCIndices[C] = SCCIndex;
C->OuterRefSCC = &RC;
}
// FIXME: We re-walk the edges in each RefSCC to establish whether it is
// a leaf and connect it to the rest of the graph's parents lists. This is
// really wasteful. We should instead do this during the DFS to avoid yet
// another edge walk.
for (RefSCC *RC : Result)
G->connectRefSCC(*RC);
// Now erase all but the root's SCCs.
SCCs.erase(remove_if(SCCs,
[&](SCC *C) {
return PostOrderMapping.lookup(&*C->begin()) !=
RootPostOrderNumber;
}),
SCCs.end());
SCCIndices.clear();
for (int i = 0, Size = SCCs.size(); i < Size; ++i)
SCCIndices[SCCs[i]] = i;
#ifndef NDEBUG
// Now we need to reconnect the current (root) SCC to the graph. We do this
// manually because we can special case our leaf handling and detect errors.
bool IsLeaf = true;
#endif
for (SCC *C : SCCs)
for (Node &N : *C) {
for (Edge &E : *N) {
RefSCC &ChildRC = *G->lookupRefSCC(E.getNode());
if (&ChildRC == this)
continue;
ChildRC.Parents.insert(this);
#ifndef NDEBUG
IsLeaf = false;
#endif
}
}
#ifndef NDEBUG
if (!Result.empty())
assert(!IsLeaf && "This SCC cannot be a leaf as we have split out new "
"SCCs by removing this edge.");
if (none_of(G->LeafRefSCCs, [&](RefSCC *C) { return C == this; }))
assert(!IsLeaf && "This SCC cannot be a leaf as it already had child "
"SCCs before we removed this edge.");
#endif
// And connect both this RefSCC and all the new ones to the correct parents.
// The easiest way to do this is just to re-analyze the old parent set.
SmallVector<RefSCC *, 4> OldParents(Parents.begin(), Parents.end());
Parents.clear();
for (RefSCC *ParentRC : OldParents)
for (SCC &ParentC : *ParentRC)
for (Node &ParentN : ParentC)
for (Edge &E : *ParentN) {
RefSCC &RC = *G->lookupRefSCC(E.getNode());
if (&RC != ParentRC)
RC.Parents.insert(ParentRC);
}
// If this SCC stopped being a leaf through this edge removal, remove it from
// the leaf SCC list. Note that this DTRT in the case where this was never
// a leaf.
// FIXME: As LeafRefSCCs could be very large, we might want to not walk the
// entire list if this RefSCC wasn't a leaf before the edge removal.
if (!Result.empty())
G->LeafRefSCCs.erase(
std::remove(G->LeafRefSCCs.begin(), G->LeafRefSCCs.end(), this),
G->LeafRefSCCs.end());
#ifndef NDEBUG
// Verify all of the new RefSCCs.
for (RefSCC *RC : Result)
RC->verify();
#endif
// Return the new list of SCCs.
return Result;
}
void LazyCallGraph::RefSCC::handleTrivialEdgeInsertion(Node &SourceN,
Node &TargetN) {
// The only trivial case that requires any graph updates is when we add new
// ref edge and may connect different RefSCCs along that path. This is only
// because of the parents set. Every other part of the graph remains constant
// after this edge insertion.
assert(G->lookupRefSCC(SourceN) == this && "Source must be in this RefSCC.");
RefSCC &TargetRC = *G->lookupRefSCC(TargetN);
if (&TargetRC == this) {
return;
}
#ifdef EXPENSIVE_CEHCKS
assert(TargetRC.isDescendantOf(*this) &&
"Target must be a descendant of the Source.");
#endif
// The only change required is to add this RefSCC to the parent set of the
// target. This is a set and so idempotent if the edge already existed.
TargetRC.Parents.insert(this);
}
void LazyCallGraph::RefSCC::insertTrivialCallEdge(Node &SourceN,
Node &TargetN) {
#ifndef NDEBUG
// Check that the RefSCC is still valid when we finish.
auto ExitVerifier = make_scope_exit([this] { verify(); });
#ifdef EXPENSIVE_CHECKS
// Check that we aren't breaking some invariants of the SCC graph. Note that
// this is quadratic in the number of edges in the call graph!
SCC &SourceC = *G->lookupSCC(SourceN);
SCC &TargetC = *G->lookupSCC(TargetN);
if (&SourceC != &TargetC)
assert(SourceC.isAncestorOf(TargetC) &&
"Call edge is not trivial in the SCC graph!");
#endif // EXPENSIVE_CHECKS
#endif // NDEBUG
// First insert it into the source or find the existing edge.
auto InsertResult =
SourceN->EdgeIndexMap.insert({&TargetN, SourceN->Edges.size()});
if (!InsertResult.second) {
// Already an edge, just update it.
Edge &E = SourceN->Edges[InsertResult.first->second];
if (E.isCall())
return; // Nothing to do!
E.setKind(Edge::Call);
} else {
// Create the new edge.
SourceN->Edges.emplace_back(TargetN, Edge::Call);
}
// Now that we have the edge, handle the graph fallout.
handleTrivialEdgeInsertion(SourceN, TargetN);
}
void LazyCallGraph::RefSCC::insertTrivialRefEdge(Node &SourceN, Node &TargetN) {
#ifndef NDEBUG
// Check that the RefSCC is still valid when we finish.
auto ExitVerifier = make_scope_exit([this] { verify(); });
#ifdef EXPENSIVE_CHECKS
// Check that we aren't breaking some invariants of the RefSCC graph.
RefSCC &SourceRC = *G->lookupRefSCC(SourceN);
RefSCC &TargetRC = *G->lookupRefSCC(TargetN);
if (&SourceRC != &TargetRC)
assert(SourceRC.isAncestorOf(TargetRC) &&
"Ref edge is not trivial in the RefSCC graph!");
#endif // EXPENSIVE_CHECKS
#endif // NDEBUG
// First insert it into the source or find the existing edge.
auto InsertResult =
SourceN->EdgeIndexMap.insert({&TargetN, SourceN->Edges.size()});
if (!InsertResult.second)
// Already an edge, we're done.
return;
// Create the new edge.
SourceN->Edges.emplace_back(TargetN, Edge::Ref);
// Now that we have the edge, handle the graph fallout.
handleTrivialEdgeInsertion(SourceN, TargetN);
}
void LazyCallGraph::RefSCC::replaceNodeFunction(Node &N, Function &NewF) {
Function &OldF = N.getFunction();
#ifndef NDEBUG
// Check that the RefSCC is still valid when we finish.
auto ExitVerifier = make_scope_exit([this] { verify(); });
assert(G->lookupRefSCC(N) == this &&
"Cannot replace the function of a node outside this RefSCC.");
assert(G->NodeMap.find(&NewF) == G->NodeMap.end() &&
"Must not have already walked the new function!'");
// It is important that this replacement not introduce graph changes so we
// insist that the caller has already removed every use of the original
// function and that all uses of the new function correspond to existing
// edges in the graph. The common and expected way to use this is when
// replacing the function itself in the IR without changing the call graph
// shape and just updating the analysis based on that.
assert(&OldF != &NewF && "Cannot replace a function with itself!");
assert(OldF.use_empty() &&
"Must have moved all uses from the old function to the new!");
#endif
N.replaceFunction(NewF);
// Update various call graph maps.
G->NodeMap.erase(&OldF);
G->NodeMap[&NewF] = &N;
}
void LazyCallGraph::insertEdge(Node &SourceN, Node &TargetN, Edge::Kind EK) {
assert(SCCMap.empty() &&
"This method cannot be called after SCCs have been formed!");
return SourceN->insertEdgeInternal(TargetN, EK);
}
void LazyCallGraph::removeEdge(Node &SourceN, Node &TargetN) {
assert(SCCMap.empty() &&
"This method cannot be called after SCCs have been formed!");
bool Removed = SourceN->removeEdgeInternal(TargetN);
(void)Removed;
assert(Removed && "Target not in the edge set for this caller?");
}
void LazyCallGraph::removeDeadFunction(Function &F) {
// FIXME: This is unnecessarily restrictive. We should be able to remove
// functions which recursively call themselves.
assert(F.use_empty() &&
"This routine should only be called on trivially dead functions!");
auto NI = NodeMap.find(&F);
if (NI == NodeMap.end())
// Not in the graph at all!
return;
Node &N = *NI->second;
NodeMap.erase(NI);
// Remove this from the entry edges if present.
EntryEdges.removeEdgeInternal(N);
if (SCCMap.empty()) {
// No SCCs have been formed, so removing this is fine and there is nothing
// else necessary at this point but clearing out the node.
N.clear();
return;
}
// Cannot remove a function which has yet to be visited in the DFS walk, so
// if we have a node at all then we must have an SCC and RefSCC.
auto CI = SCCMap.find(&N);
assert(CI != SCCMap.end() &&
"Tried to remove a node without an SCC after DFS walk started!");
SCC &C = *CI->second;
SCCMap.erase(CI);
RefSCC &RC = C.getOuterRefSCC();
// This node must be the only member of its SCC as it has no callers, and
// that SCC must be the only member of a RefSCC as it has no references.
// Validate these properties first.
assert(C.size() == 1 && "Dead functions must be in a singular SCC");
assert(RC.size() == 1 && "Dead functions must be in a singular RefSCC");
// Clean up any remaining reference edges. Note that we walk an unordered set
// here but are just removing and so the order doesn't matter.
for (RefSCC &ParentRC : RC.parents())
for (SCC &ParentC : ParentRC)
for (Node &ParentN : ParentC)
if (ParentN)
ParentN->removeEdgeInternal(N);
// Now remove this RefSCC from any parents sets and the leaf list.
for (Edge &E : *N)
if (RefSCC *TargetRC = lookupRefSCC(E.getNode()))
TargetRC->Parents.erase(&RC);
// FIXME: This is a linear operation which could become hot and benefit from
// an index map.
auto LRI = find(LeafRefSCCs, &RC);
if (LRI != LeafRefSCCs.end())
LeafRefSCCs.erase(LRI);
auto RCIndexI = RefSCCIndices.find(&RC);
int RCIndex = RCIndexI->second;
PostOrderRefSCCs.erase(PostOrderRefSCCs.begin() + RCIndex);
RefSCCIndices.erase(RCIndexI);
for (int i = RCIndex, Size = PostOrderRefSCCs.size(); i < Size; ++i)
RefSCCIndices[PostOrderRefSCCs[i]] = i;
// Finally clear out all the data structures from the node down through the
// components.
N.clear();
C.clear();
RC.clear();
// Nothing to delete as all the objects are allocated in stable bump pointer
// allocators.
}
LazyCallGraph::Node &LazyCallGraph::insertInto(Function &F, Node *&MappedN) {
return *new (MappedN = BPA.Allocate()) Node(*this, F);
}
void LazyCallGraph::updateGraphPtrs() {
// Process all nodes updating the graph pointers.
{
SmallVector<Node *, 16> Worklist;
for (Edge &E : EntryEdges)
Worklist.push_back(&E.getNode());
while (!Worklist.empty()) {
Node &N = *Worklist.pop_back_val();
N.G = this;
if (N)
for (Edge &E : *N)
Worklist.push_back(&E.getNode());
}
}
// Process all SCCs updating the graph pointers.
{
SmallVector<RefSCC *, 16> Worklist(LeafRefSCCs.begin(), LeafRefSCCs.end());
while (!Worklist.empty()) {
RefSCC &C = *Worklist.pop_back_val();
C.G = this;
for (RefSCC &ParentC : C.parents())
Worklist.push_back(&ParentC);
}
}
}
template <typename RootsT, typename GetBeginT, typename GetEndT,
typename GetNodeT, typename FormSCCCallbackT>
void LazyCallGraph::buildGenericSCCs(RootsT &&Roots, GetBeginT &&GetBegin,
GetEndT &&GetEnd, GetNodeT &&GetNode,
FormSCCCallbackT &&FormSCC) {
typedef decltype(GetBegin(std::declval<Node &>())) EdgeItT;
SmallVector<std::pair<Node *, EdgeItT>, 16> DFSStack;
SmallVector<Node *, 16> PendingSCCStack;
// Scan down the stack and DFS across the call edges.
for (Node *RootN : Roots) {
assert(DFSStack.empty() &&
"Cannot begin a new root with a non-empty DFS stack!");
assert(PendingSCCStack.empty() &&
"Cannot begin a new root with pending nodes for an SCC!");
// Skip any nodes we've already reached in the DFS.
if (RootN->DFSNumber != 0) {
assert(RootN->DFSNumber == -1 &&
"Shouldn't have any mid-DFS root nodes!");
continue;
}
RootN->DFSNumber = RootN->LowLink = 1;
int NextDFSNumber = 2;
DFSStack.push_back({RootN, GetBegin(*RootN)});
do {
Node *N;
EdgeItT I;
std::tie(N, I) = DFSStack.pop_back_val();
auto E = GetEnd(*N);
while (I != E) {
Node &ChildN = GetNode(I);
if (ChildN.DFSNumber == 0) {
// We haven't yet visited this child, so descend, pushing the current
// node onto the stack.
DFSStack.push_back({N, I});
ChildN.DFSNumber = ChildN.LowLink = NextDFSNumber++;
N = &ChildN;
I = GetBegin(*N);
E = GetEnd(*N);
continue;
}
// If the child has already been added to some child component, it
// couldn't impact the low-link of this parent because it isn't
// connected, and thus its low-link isn't relevant so skip it.
if (ChildN.DFSNumber == -1) {
++I;
continue;
}
// Track the lowest linked child as the lowest link for this node.
assert(ChildN.LowLink > 0 && "Must have a positive low-link number!");
if (ChildN.LowLink < N->LowLink)
N->LowLink = ChildN.LowLink;
// Move to the next edge.
++I;
}
// We've finished processing N and its descendents, put it on our pending
// SCC stack to eventually get merged into an SCC of nodes.
PendingSCCStack.push_back(N);
// If this node is linked to some lower entry, continue walking up the
// stack.
if (N->LowLink != N->DFSNumber)
continue;
// Otherwise, we've completed an SCC. Append it to our post order list of
// SCCs.
int RootDFSNumber = N->DFSNumber;
// Find the range of the node stack by walking down until we pass the
// root DFS number.
auto SCCNodes = make_range(
PendingSCCStack.rbegin(),
find_if(reverse(PendingSCCStack), [RootDFSNumber](const Node *N) {
return N->DFSNumber < RootDFSNumber;
}));
// Form a new SCC out of these nodes and then clear them off our pending
// stack.
FormSCC(SCCNodes);
PendingSCCStack.erase(SCCNodes.end().base(), PendingSCCStack.end());
} while (!DFSStack.empty());
}
}
/// Build the internal SCCs for a RefSCC from a sequence of nodes.
///
/// Appends the SCCs to the provided vector and updates the map with their
/// indices. Both the vector and map must be empty when passed into this
/// routine.
void LazyCallGraph::buildSCCs(RefSCC &RC, node_stack_range Nodes) {
assert(RC.SCCs.empty() && "Already built SCCs!");
assert(RC.SCCIndices.empty() && "Already mapped SCC indices!");
for (Node *N : Nodes) {
assert(N->LowLink >= (*Nodes.begin())->LowLink &&
"We cannot have a low link in an SCC lower than its root on the "
"stack!");
// This node will go into the next RefSCC, clear out its DFS and low link
// as we scan.
N->DFSNumber = N->LowLink = 0;
}
// Each RefSCC contains a DAG of the call SCCs. To build these, we do
// a direct walk of the call edges using Tarjan's algorithm. We reuse the
// internal storage as we won't need it for the outer graph's DFS any longer.
buildGenericSCCs(
Nodes, [](Node &N) { return N->call_begin(); },
[](Node &N) { return N->call_end(); },
[](EdgeSequence::call_iterator I) -> Node & { return I->getNode(); },
[this, &RC](node_stack_range Nodes) {
RC.SCCs.push_back(createSCC(RC, Nodes));
for (Node &N : *RC.SCCs.back()) {
N.DFSNumber = N.LowLink = -1;
SCCMap[&N] = RC.SCCs.back();
}
});
// Wire up the SCC indices.
for (int i = 0, Size = RC.SCCs.size(); i < Size; ++i)
RC.SCCIndices[RC.SCCs[i]] = i;
}
void LazyCallGraph::buildRefSCCs() {
if (EntryEdges.empty() || !PostOrderRefSCCs.empty())
// RefSCCs are either non-existent or already built!
return;
assert(RefSCCIndices.empty() && "Already mapped RefSCC indices!");
SmallVector<Node *, 16> Roots;
for (Edge &E : *this)
Roots.push_back(&E.getNode());
// The roots will be popped of a stack, so use reverse to get a less
// surprising order. This doesn't change any of the semantics anywhere.
std::reverse(Roots.begin(), Roots.end());
buildGenericSCCs(
Roots,
[](Node &N) {
// We need to populate each node as we begin to walk its edges.
N.populate();
return N->begin();
},
[](Node &N) { return N->end(); },
[](EdgeSequence::iterator I) -> Node & { return I->getNode(); },
[this](node_stack_range Nodes) {
RefSCC *NewRC = createRefSCC(*this);
buildSCCs(*NewRC, Nodes);
connectRefSCC(*NewRC);
// Push the new node into the postorder list and remember its position
// in the index map.
bool Inserted =
RefSCCIndices.insert({NewRC, PostOrderRefSCCs.size()}).second;
(void)Inserted;
assert(Inserted && "Cannot already have this RefSCC in the index map!");
PostOrderRefSCCs.push_back(NewRC);
#ifndef NDEBUG
NewRC->verify();
#endif
});
}
// FIXME: We should move callers of this to embed the parent linking and leaf
// tracking into their DFS in order to remove a full walk of all edges.
void LazyCallGraph::connectRefSCC(RefSCC &RC) {
// Walk all edges in the RefSCC (this remains linear as we only do this once
// when we build the RefSCC) to connect it to the parent sets of its
// children.
bool IsLeaf = true;
for (SCC &C : RC)
for (Node &N : C)
for (Edge &E : *N) {
RefSCC &ChildRC = *lookupRefSCC(E.getNode());
if (&ChildRC == &RC)
continue;
ChildRC.Parents.insert(&RC);
IsLeaf = false;
}
// For the SCCs where we find no child SCCs, add them to the leaf list.
if (IsLeaf)
LeafRefSCCs.push_back(&RC);
}
AnalysisKey LazyCallGraphAnalysis::Key;
LazyCallGraphPrinterPass::LazyCallGraphPrinterPass(raw_ostream &OS) : OS(OS) {}
static void printNode(raw_ostream &OS, LazyCallGraph::Node &N) {
OS << " Edges in function: " << N.getFunction().getName() << "\n";
for (LazyCallGraph::Edge &E : N.populate())
OS << " " << (E.isCall() ? "call" : "ref ") << " -> "
<< E.getFunction().getName() << "\n";
OS << "\n";
}
static void printSCC(raw_ostream &OS, LazyCallGraph::SCC &C) {
ptrdiff_t Size = std::distance(C.begin(), C.end());
OS << " SCC with " << Size << " functions:\n";
for (LazyCallGraph::Node &N : C)
OS << " " << N.getFunction().getName() << "\n";
}
static void printRefSCC(raw_ostream &OS, LazyCallGraph::RefSCC &C) {
ptrdiff_t Size = std::distance(C.begin(), C.end());
OS << " RefSCC with " << Size << " call SCCs:\n";
for (LazyCallGraph::SCC &InnerC : C)
printSCC(OS, InnerC);
OS << "\n";
}
PreservedAnalyses LazyCallGraphPrinterPass::run(Module &M,
ModuleAnalysisManager &AM) {
LazyCallGraph &G = AM.getResult<LazyCallGraphAnalysis>(M);
OS << "Printing the call graph for module: " << M.getModuleIdentifier()
<< "\n\n";
for (Function &F : M)
printNode(OS, G.get(F));
G.buildRefSCCs();
for (LazyCallGraph::RefSCC &C : G.postorder_ref_sccs())
printRefSCC(OS, C);
return PreservedAnalyses::all();
}
LazyCallGraphDOTPrinterPass::LazyCallGraphDOTPrinterPass(raw_ostream &OS)
: OS(OS) {}
static void printNodeDOT(raw_ostream &OS, LazyCallGraph::Node &N) {
std::string Name = "\"" + DOT::EscapeString(N.getFunction().getName()) + "\"";
for (LazyCallGraph::Edge &E : N.populate()) {
OS << " " << Name << " -> \""
<< DOT::EscapeString(E.getFunction().getName()) << "\"";
if (!E.isCall()) // It is a ref edge.
OS << " [style=dashed,label=\"ref\"]";
OS << ";\n";
}
OS << "\n";
}
PreservedAnalyses LazyCallGraphDOTPrinterPass::run(Module &M,
ModuleAnalysisManager &AM) {
LazyCallGraph &G = AM.getResult<LazyCallGraphAnalysis>(M);
OS << "digraph \"" << DOT::EscapeString(M.getModuleIdentifier()) << "\" {\n";
for (Function &F : M)
printNodeDOT(OS, G.get(F));
OS << "}\n";
return PreservedAnalyses::all();
}
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