//===- 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/STLExtras.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/raw_ostream.h"
using namespace llvm;
#define DEBUG_TYPE "lcg"
static void findCallees(
SmallVectorImpl<Constant *> &Worklist, SmallPtrSetImpl<Constant *> &Visited,
SmallVectorImpl<PointerUnion<Function *, LazyCallGraph::Node *>> &Callees,
DenseMap<Function *, size_t> &CalleeIndexMap) {
while (!Worklist.empty()) {
Constant *C = Worklist.pop_back_val();
if (Function *F = dyn_cast<Function>(C)) {
// 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.
if (!F->isDeclaration() &&
CalleeIndexMap.insert(std::make_pair(F, Callees.size())).second) {
DEBUG(dbgs() << " Added callable function: " << F->getName()
<< "\n");
Callees.push_back(F);
}
continue;
}
for (Value *Op : C->operand_values())
if (Visited.insert(cast<Constant>(Op)).second)
Worklist.push_back(cast<Constant>(Op));
}
}
LazyCallGraph::Node::Node(LazyCallGraph &G, Function &F)
: G(&G), F(F), DFSNumber(0), LowLink(0) {
DEBUG(dbgs() << " Adding functions called by '" << F.getName()
<< "' to the graph.\n");
SmallVector<Constant *, 16> Worklist;
SmallPtrSet<Constant *, 16> Visited;
// Find all the potential callees in this function. First walk the
// instructions and add every operand which is a constant to the worklist.
for (BasicBlock &BB : F)
for (Instruction &I : BB)
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.
findCallees(Worklist, Visited, Callees, CalleeIndexMap);
}
void LazyCallGraph::Node::insertEdgeInternal(Function &Callee) {
if (Node *N = G->lookup(Callee))
return insertEdgeInternal(*N);
CalleeIndexMap.insert(std::make_pair(&Callee, Callees.size()));
Callees.push_back(&Callee);
}
void LazyCallGraph::Node::insertEdgeInternal(Node &CalleeN) {
CalleeIndexMap.insert(std::make_pair(&CalleeN.getFunction(), Callees.size()));
Callees.push_back(&CalleeN);
}
void LazyCallGraph::Node::removeEdgeInternal(Function &Callee) {
auto IndexMapI = CalleeIndexMap.find(&Callee);
assert(IndexMapI != CalleeIndexMap.end() &&
"Callee not in the callee set for this caller?");
Callees[IndexMapI->second] = nullptr;
CalleeIndexMap.erase(IndexMapI);
}
LazyCallGraph::LazyCallGraph(Module &M) : NextDFSNumber(0) {
DEBUG(dbgs() << "Building CG for module: " << M.getModuleIdentifier()
<< "\n");
for (Function &F : M)
if (!F.isDeclaration() && !F.hasLocalLinkage())
if (EntryIndexMap.insert(std::make_pair(&F, EntryNodes.size())).second) {
DEBUG(dbgs() << " Adding '" << F.getName()
<< "' to entry set of the graph.\n");
EntryNodes.push_back(&F);
}
// 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");
findCallees(Worklist, Visited, EntryNodes, EntryIndexMap);
for (auto &Entry : EntryNodes) {
assert(!Entry.isNull() &&
"We can't have removed edges before we finish the constructor!");
if (Function *F = Entry.dyn_cast<Function *>())
SCCEntryNodes.push_back(F);
else
SCCEntryNodes.push_back(&Entry.get<Node *>()->getFunction());
}
}
LazyCallGraph::LazyCallGraph(LazyCallGraph &&G)
: BPA(std::move(G.BPA)), NodeMap(std::move(G.NodeMap)),
EntryNodes(std::move(G.EntryNodes)),
EntryIndexMap(std::move(G.EntryIndexMap)), SCCBPA(std::move(G.SCCBPA)),
SCCMap(std::move(G.SCCMap)), LeafSCCs(std::move(G.LeafSCCs)),
DFSStack(std::move(G.DFSStack)),
SCCEntryNodes(std::move(G.SCCEntryNodes)),
NextDFSNumber(G.NextDFSNumber) {
updateGraphPtrs();
}
LazyCallGraph &LazyCallGraph::operator=(LazyCallGraph &&G) {
BPA = std::move(G.BPA);
NodeMap = std::move(G.NodeMap);
EntryNodes = std::move(G.EntryNodes);
EntryIndexMap = std::move(G.EntryIndexMap);
SCCBPA = std::move(G.SCCBPA);
SCCMap = std::move(G.SCCMap);
LeafSCCs = std::move(G.LeafSCCs);
DFSStack = std::move(G.DFSStack);
SCCEntryNodes = std::move(G.SCCEntryNodes);
NextDFSNumber = G.NextDFSNumber;
updateGraphPtrs();
return *this;
}
void LazyCallGraph::SCC::insert(Node &N) {
N.DFSNumber = N.LowLink = -1;
Nodes.push_back(&N);
G->SCCMap[&N] = this;
}
bool LazyCallGraph::SCC::isDescendantOf(const SCC &C) const {
// Walk up the parents of this SCC and verify that we eventually find C.
SmallVector<const SCC *, 4> AncestorWorklist;
AncestorWorklist.push_back(this);
do {
const SCC *AncestorC = AncestorWorklist.pop_back_val();
if (AncestorC->isChildOf(C))
return true;
for (const SCC *ParentC : AncestorC->ParentSCCs)
AncestorWorklist.push_back(ParentC);
} while (!AncestorWorklist.empty());
return false;
}
void LazyCallGraph::SCC::insertIntraSCCEdge(Node &CallerN, Node &CalleeN) {
// First insert it into the caller.
CallerN.insertEdgeInternal(CalleeN);
assert(G->SCCMap.lookup(&CallerN) == this && "Caller must be in this SCC.");
assert(G->SCCMap.lookup(&CalleeN) == this && "Callee must be in this SCC.");
// Nothing changes about this SCC or any other.
}
void LazyCallGraph::SCC::insertOutgoingEdge(Node &CallerN, Node &CalleeN) {
// First insert it into the caller.
CallerN.insertEdgeInternal(CalleeN);
assert(G->SCCMap.lookup(&CallerN) == this && "Caller must be in this SCC.");
SCC &CalleeC = *G->SCCMap.lookup(&CalleeN);
assert(&CalleeC != this && "Callee must not be in this SCC.");
assert(CalleeC.isDescendantOf(*this) &&
"Callee must be a descendant of the Caller.");
// The only change required is to add this SCC to the parent set of the callee.
CalleeC.ParentSCCs.insert(this);
}
SmallVector<LazyCallGraph::SCC *, 1>
LazyCallGraph::SCC::insertIncomingEdge(Node &CallerN, Node &CalleeN) {
// First insert it into the caller.
CallerN.insertEdgeInternal(CalleeN);
assert(G->SCCMap.lookup(&CalleeN) == this && "Callee must be in this SCC.");
SCC &CallerC = *G->SCCMap.lookup(&CallerN);
assert(&CallerC != this && "Caller must not be in this SCC.");
assert(CallerC.isDescendantOf(*this) &&
"Caller must be a descendant of the Callee.");
// The algorithm we use for merging SCCs based on the cycle introduced here
// is to walk the SCC inverted DAG formed by the parent SCC sets. The inverse
// graph has the same cycle properties as the actual DAG of the SCCs, and
// when forming SCCs lazily by a DFS, the bottom of the graph won't exist in
// many cases which should prune the search space.
//
// FIXME: We can get this pruning behavior even after the incremental SCC
// formation by leaving behind (conservative) DFS numberings in the nodes,
// and pruning the search with them. These would need to be cleverly updated
// during the removal of intra-SCC edges, but could be preserved
// conservatively.
// The set of SCCs that are connected to the caller, and thus will
// participate in the merged connected component.
SmallPtrSet<SCC *, 8> ConnectedSCCs;
ConnectedSCCs.insert(this);
ConnectedSCCs.insert(&CallerC);
// We build up a DFS stack of the parents chains.
SmallVector<std::pair<SCC *, SCC::parent_iterator>, 8> DFSSCCs;
SmallPtrSet<SCC *, 8> VisitedSCCs;
int ConnectedDepth = -1;
SCC *C = this;
parent_iterator I = parent_begin(), E = parent_end();
for (;;) {
while (I != E) {
SCC &ParentSCC = *I++;
// If we have already processed this parent SCC, skip it, and remember
// whether it was connected so we don't have to check the rest of the
// stack. This also handles when we reach a child of the 'this' SCC (the
// callee) which terminates the search.
if (ConnectedSCCs.count(&ParentSCC)) {
ConnectedDepth = std::max<int>(ConnectedDepth, DFSSCCs.size());
continue;
}
if (VisitedSCCs.count(&ParentSCC))
continue;
// We fully explore the depth-first space, adding nodes to the connected
// set only as we pop them off, so "recurse" by rotating to the parent.
DFSSCCs.push_back(std::make_pair(C, I));
C = &ParentSCC;
I = ParentSCC.parent_begin();
E = ParentSCC.parent_end();
}
// If we've found a connection anywhere below this point on the stack (and
// thus up the parent graph from the caller), the current node needs to be
// added to the connected set now that we've processed all of its parents.
if ((int)DFSSCCs.size() == ConnectedDepth) {
--ConnectedDepth; // We're finished with this connection.
ConnectedSCCs.insert(C);
} else {
// Otherwise remember that its parents don't ever connect.
assert(ConnectedDepth < (int)DFSSCCs.size() &&
"Cannot have a connected depth greater than the DFS depth!");
VisitedSCCs.insert(C);
}
if (DFSSCCs.empty())
break; // We've walked all the parents of the caller transitively.
// Pop off the prior node and position to unwind the depth first recursion.
std::tie(C, I) = DFSSCCs.pop_back_val();
E = C->parent_end();
}
// 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.
// FIXME: This operation currently creates ordering stability problems
// because we don't use stably ordered containers for the parent SCCs or the
// connected SCCs.
unsigned NewNodeBeginIdx = Nodes.size();
for (SCC *C : ConnectedSCCs) {
if (C == this)
continue;
for (SCC *ParentC : C->ParentSCCs)
if (!ConnectedSCCs.count(ParentC))
ParentSCCs.insert(ParentC);
C->ParentSCCs.clear();
for (Node *N : *C) {
for (Node &ChildN : *N) {
SCC &ChildC = *G->SCCMap.lookup(&ChildN);
if (&ChildC != C)
ChildC.ParentSCCs.erase(C);
}
G->SCCMap[N] = this;
Nodes.push_back(N);
}
C->Nodes.clear();
}
for (auto I = Nodes.begin() + NewNodeBeginIdx, E = Nodes.end(); I != E; ++I)
for (Node &ChildN : **I) {
SCC &ChildC = *G->SCCMap.lookup(&ChildN);
if (&ChildC != this)
ChildC.ParentSCCs.insert(this);
}
// 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 SmallVector<SCC *, 1>(ConnectedSCCs.begin(), ConnectedSCCs.end());
}
void LazyCallGraph::SCC::removeInterSCCEdge(Node &CallerN, Node &CalleeN) {
// First remove it from the node.
CallerN.removeEdgeInternal(CalleeN.getFunction());
assert(G->SCCMap.lookup(&CallerN) == this &&
"The caller must be a member of this SCC.");
SCC &CalleeC = *G->SCCMap.lookup(&CalleeN);
assert(&CalleeC != this &&
"This API only supports the rmoval of inter-SCC edges.");
assert(std::find(G->LeafSCCs.begin(), G->LeafSCCs.end(), this) ==
G->LeafSCCs.end() &&
"Cannot have a leaf SCC caller with a different SCC callee.");
bool HasOtherCallToCalleeC = false;
bool HasOtherCallOutsideSCC = false;
for (Node *N : *this) {
for (Node &OtherCalleeN : *N) {
SCC &OtherCalleeC = *G->SCCMap.lookup(&OtherCalleeN);
if (&OtherCalleeC == &CalleeC) {
HasOtherCallToCalleeC = true;
break;
}
if (&OtherCalleeC != this)
HasOtherCallOutsideSCC = true;
}
if (HasOtherCallToCalleeC)
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 caller no longer a parent of the callee. Walk the other call edges
// in the caller to tell.
if (!HasOtherCallToCalleeC) {
bool Removed = CalleeC.ParentSCCs.erase(this);
(void)Removed;
assert(Removed &&
"Did not find the caller SCC in the callee 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 (CalleeC.ParentSCCs.empty())
DEBUG(dbgs() << "LCG: Update removing " << CallerN.getFunction().getName()
<< " -> " << CalleeN.getFunction().getName()
<< " edge orphaned the callee's SCC!\n");
}
// It may make the Caller SCC a leaf SCC.
if (!HasOtherCallOutsideSCC)
G->LeafSCCs.push_back(this);
}
void LazyCallGraph::SCC::internalDFS(
SmallVectorImpl<std::pair<Node *, Node::iterator>> &DFSStack,
SmallVectorImpl<Node *> &PendingSCCStack, Node *N,
SmallVectorImpl<SCC *> &ResultSCCs) {
Node::iterator I = N->begin();
N->LowLink = N->DFSNumber = 1;
int NextDFSNumber = 2;
for (;;) {
assert(N->DFSNumber != 0 && "We should always assign a DFS number "
"before processing a node.");
// We simulate recursion by popping out of the nested loop and continuing.
Node::iterator E = N->end();
while (I != E) {
Node &ChildN = *I;
if (SCC *ChildSCC = G->SCCMap.lookup(&ChildN)) {
// Check if we have reached a node in the new (known connected) set of
// this SCC. If so, the entire stack is necessarily in that set and we
// can re-start.
if (ChildSCC == this) {
insert(*N);
while (!PendingSCCStack.empty())
insert(*PendingSCCStack.pop_back_val());
while (!DFSStack.empty())
insert(*DFSStack.pop_back_val().first);
return;
}
// If this child isn't currently in this SCC, no need to process it.
// However, we do need to remove this SCC from its SCC's parent set.
ChildSCC->ParentSCCs.erase(this);
++I;
continue;
}
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(std::make_pair(N, I));
// Continue, resetting to the child node.
ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
N = &ChildN;
I = ChildN.begin();
E = ChildN.end();
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->LowLink == N->DFSNumber) {
ResultSCCs.push_back(G->formSCC(N, PendingSCCStack));
if (DFSStack.empty())
return;
} else {
// At this point we know that N cannot ever be an SCC root. Its low-link
// is not its dfs-number, and we've processed all of its children. It is
// just sitting here waiting until some node further down the stack gets
// low-link == dfs-number and pops it off as well. Move it to the pending
// stack which is pulled into the next SCC to be formed.
PendingSCCStack.push_back(N);
assert(!DFSStack.empty() && "We shouldn't have an empty stack!");
}
N = DFSStack.back().first;
I = DFSStack.back().second;
DFSStack.pop_back();
}
}
SmallVector<LazyCallGraph::SCC *, 1>
LazyCallGraph::SCC::removeIntraSCCEdge(Node &CallerN,
Node &CalleeN) {
// First remove it from the node.
CallerN.removeEdgeInternal(CalleeN.getFunction());
// We return a list of the resulting *new* SCCs in postorder.
SmallVector<SCC *, 1> ResultSCCs;
// Direct recursion doesn't impact the SCC graph at all.
if (&CallerN == &CalleeN)
return ResultSCCs;
// The worklist is every node in the original SCC.
SmallVector<Node *, 1> Worklist;
Worklist.swap(Nodes);
for (Node *N : Worklist) {
// The nodes formerly in this SCC are no longer in any SCC.
N->DFSNumber = 0;
N->LowLink = 0;
G->SCCMap.erase(N);
}
assert(Worklist.size() > 1 && "We have to have at least two nodes to have an "
"edge between them that is within the SCC.");
// The callee can already reach every node in this SCC (by definition). It is
// the only node we know will stay inside this SCC. Everything which
// transitively reaches Callee will also remain in the SCC. To model this we
// incrementally add any chain of nodes which reaches something in the new
// node set to the new node set. This short circuits one side of the Tarjan's
// walk.
insert(CalleeN);
// We're going to do a full mini-Tarjan's walk using a local stack here.
SmallVector<std::pair<Node *, Node::iterator>, 4> DFSStack;
SmallVector<Node *, 4> PendingSCCStack;
do {
Node *N = Worklist.pop_back_val();
if (N->DFSNumber == 0)
internalDFS(DFSStack, PendingSCCStack, N, ResultSCCs);
assert(DFSStack.empty() && "Didn't flush the entire DFS stack!");
assert(PendingSCCStack.empty() && "Didn't flush all pending SCC nodes!");
} while (!Worklist.empty());
// Now we need to reconnect the current SCC to the graph.
bool IsLeafSCC = true;
for (Node *N : Nodes) {
for (Node &ChildN : *N) {
SCC &ChildSCC = *G->SCCMap.lookup(&ChildN);
if (&ChildSCC == this)
continue;
ChildSCC.ParentSCCs.insert(this);
IsLeafSCC = false;
}
}
#ifndef NDEBUG
if (!ResultSCCs.empty())
assert(!IsLeafSCC && "This SCC cannot be a leaf as we have split out new "
"SCCs by removing this edge.");
if (!std::any_of(G->LeafSCCs.begin(), G->LeafSCCs.end(),
[&](SCC *C) { return C == this; }))
assert(!IsLeafSCC && "This SCC cannot be a leaf as it already had child "
"SCCs before we removed this edge.");
#endif
// If this SCC stopped being a leaf through this edge removal, remove it from
// the leaf SCC list.
if (!IsLeafSCC && !ResultSCCs.empty())
G->LeafSCCs.erase(std::remove(G->LeafSCCs.begin(), G->LeafSCCs.end(), this),
G->LeafSCCs.end());
// Return the new list of SCCs.
return ResultSCCs;
}
void LazyCallGraph::insertEdge(Node &CallerN, Function &Callee) {
assert(SCCMap.empty() && DFSStack.empty() &&
"This method cannot be called after SCCs have been formed!");
return CallerN.insertEdgeInternal(Callee);
}
void LazyCallGraph::removeEdge(Node &CallerN, Function &Callee) {
assert(SCCMap.empty() && DFSStack.empty() &&
"This method cannot be called after SCCs have been formed!");
return CallerN.removeEdgeInternal(Callee);
}
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 (auto &Entry : EntryNodes)
if (Node *EntryN = Entry.dyn_cast<Node *>())
Worklist.push_back(EntryN);
while (!Worklist.empty()) {
Node *N = Worklist.pop_back_val();
N->G = this;
for (auto &Callee : N->Callees)
if (!Callee.isNull())
if (Node *CalleeN = Callee.dyn_cast<Node *>())
Worklist.push_back(CalleeN);
}
}
// Process all SCCs updating the graph pointers.
{
SmallVector<SCC *, 16> Worklist(LeafSCCs.begin(), LeafSCCs.end());
while (!Worklist.empty()) {
SCC *C = Worklist.pop_back_val();
C->G = this;
Worklist.insert(Worklist.end(), C->ParentSCCs.begin(),
C->ParentSCCs.end());
}
}
}
LazyCallGraph::SCC *LazyCallGraph::formSCC(Node *RootN,
SmallVectorImpl<Node *> &NodeStack) {
// The tail of the stack is the new SCC. Allocate the SCC and pop the stack
// into it.
SCC *NewSCC = new (SCCBPA.Allocate()) SCC(*this);
while (!NodeStack.empty() && NodeStack.back()->DFSNumber > RootN->DFSNumber) {
assert(NodeStack.back()->LowLink >= RootN->LowLink &&
"We cannot have a low link in an SCC lower than its root on the "
"stack!");
NewSCC->insert(*NodeStack.pop_back_val());
}
NewSCC->insert(*RootN);
// A final pass over all edges in the SCC (this remains linear as we only
// do this once when we build the SCC) to connect it to the parent sets of
// its children.
bool IsLeafSCC = true;
for (Node *SCCN : NewSCC->Nodes)
for (Node &SCCChildN : *SCCN) {
SCC &ChildSCC = *SCCMap.lookup(&SCCChildN);
if (&ChildSCC == NewSCC)
continue;
ChildSCC.ParentSCCs.insert(NewSCC);
IsLeafSCC = false;
}
// For the SCCs where we fine no child SCCs, add them to the leaf list.
if (IsLeafSCC)
LeafSCCs.push_back(NewSCC);
return NewSCC;
}
LazyCallGraph::SCC *LazyCallGraph::getNextSCCInPostOrder() {
Node *N;
Node::iterator I;
if (!DFSStack.empty()) {
N = DFSStack.back().first;
I = DFSStack.back().second;
DFSStack.pop_back();
} else {
// If we've handled all candidate entry nodes to the SCC forest, we're done.
do {
if (SCCEntryNodes.empty())
return nullptr;
N = &get(*SCCEntryNodes.pop_back_val());
} while (N->DFSNumber != 0);
I = N->begin();
N->LowLink = N->DFSNumber = 1;
NextDFSNumber = 2;
}
for (;;) {
assert(N->DFSNumber != 0 && "We should always assign a DFS number "
"before placing a node onto the stack.");
Node::iterator E = N->end();
while (I != E) {
Node &ChildN = *I;
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(std::make_pair(N, N->begin()));
// Recurse onto this node via a tail call.
assert(!SCCMap.count(&ChildN) &&
"Found a node with 0 DFS number but already in an SCC!");
ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
N = &ChildN;
I = ChildN.begin();
E = ChildN.end();
continue;
}
// Track the lowest link of the children, if any are still in the stack.
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->LowLink == N->DFSNumber)
// Form the new SCC out of the top of the DFS stack.
return formSCC(N, PendingSCCStack);
// At this point we know that N cannot ever be an SCC root. Its low-link
// is not its dfs-number, and we've processed all of its children. It is
// just sitting here waiting until some node further down the stack gets
// low-link == dfs-number and pops it off as well. Move it to the pending
// stack which is pulled into the next SCC to be formed.
PendingSCCStack.push_back(N);
assert(!DFSStack.empty() && "We never found a viable root!");
N = DFSStack.back().first;
I = DFSStack.back().second;
DFSStack.pop_back();
}
}
char LazyCallGraphAnalysis::PassID;
LazyCallGraphPrinterPass::LazyCallGraphPrinterPass(raw_ostream &OS) : OS(OS) {}
static void printNodes(raw_ostream &OS, LazyCallGraph::Node &N,
SmallPtrSetImpl<LazyCallGraph::Node *> &Printed) {
// Recurse depth first through the nodes.
for (LazyCallGraph::Node &ChildN : N)
if (Printed.insert(&ChildN).second)
printNodes(OS, ChildN, Printed);
OS << " Call edges in function: " << N.getFunction().getName() << "\n";
for (LazyCallGraph::iterator I = N.begin(), E = N.end(); I != E; ++I)
OS << " -> " << I->getFunction().getName() << "\n";
OS << "\n";
}
static void printSCC(raw_ostream &OS, LazyCallGraph::SCC &SCC) {
ptrdiff_t SCCSize = std::distance(SCC.begin(), SCC.end());
OS << " SCC with " << SCCSize << " functions:\n";
for (LazyCallGraph::Node *N : SCC)
OS << " " << N->getFunction().getName() << "\n";
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";
SmallPtrSet<LazyCallGraph::Node *, 16> Printed;
for (LazyCallGraph::Node &N : G)
if (Printed.insert(&N).second)
printNodes(OS, N, Printed);
for (LazyCallGraph::SCC &SCC : G.postorder_sccs())
printSCC(OS, SCC);
return PreservedAnalyses::all();
}