1 //===- LazyCallGraph.cpp - Analysis of a Module's call graph --------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 #include "llvm/Analysis/LazyCallGraph.h"
11 #include "llvm/ADT/STLExtras.h"
12 #include "llvm/IR/CallSite.h"
13 #include "llvm/IR/InstVisitor.h"
14 #include "llvm/IR/Instructions.h"
15 #include "llvm/IR/PassManager.h"
16 #include "llvm/Support/Debug.h"
17 #include "llvm/Support/raw_ostream.h"
21 #define DEBUG_TYPE "lcg"
23 static void findCallees(
24 SmallVectorImpl<Constant *> &Worklist, SmallPtrSetImpl<Constant *> &Visited,
25 SmallVectorImpl<PointerUnion<Function *, LazyCallGraph::Node *>> &Callees,
26 DenseMap<Function *, size_t> &CalleeIndexMap) {
27 while (!Worklist.empty()) {
28 Constant *C = Worklist.pop_back_val();
30 if (Function *F = dyn_cast<Function>(C)) {
31 // Note that we consider *any* function with a definition to be a viable
32 // edge. Even if the function's definition is subject to replacement by
33 // some other module (say, a weak definition) there may still be
34 // optimizations which essentially speculate based on the definition and
35 // a way to check that the specific definition is in fact the one being
36 // used. For example, this could be done by moving the weak definition to
37 // a strong (internal) definition and making the weak definition be an
38 // alias. Then a test of the address of the weak function against the new
39 // strong definition's address would be an effective way to determine the
40 // safety of optimizing a direct call edge.
41 if (!F->isDeclaration() &&
42 CalleeIndexMap.insert(std::make_pair(F, Callees.size())).second) {
43 DEBUG(dbgs() << " Added callable function: " << F->getName()
50 for (Value *Op : C->operand_values())
51 if (Visited.insert(cast<Constant>(Op)).second)
52 Worklist.push_back(cast<Constant>(Op));
56 LazyCallGraph::Node::Node(LazyCallGraph &G, Function &F)
57 : G(&G), F(F), DFSNumber(0), LowLink(0) {
58 DEBUG(dbgs() << " Adding functions called by '" << F.getName()
59 << "' to the graph.\n");
61 SmallVector<Constant *, 16> Worklist;
62 SmallPtrSet<Constant *, 16> Visited;
63 // Find all the potential callees in this function. First walk the
64 // instructions and add every operand which is a constant to the worklist.
65 for (BasicBlock &BB : F)
66 for (Instruction &I : BB)
67 for (Value *Op : I.operand_values())
68 if (Constant *C = dyn_cast<Constant>(Op))
69 if (Visited.insert(C).second)
70 Worklist.push_back(C);
72 // We've collected all the constant (and thus potentially function or
73 // function containing) operands to all of the instructions in the function.
74 // Process them (recursively) collecting every function found.
75 findCallees(Worklist, Visited, Callees, CalleeIndexMap);
78 void LazyCallGraph::Node::insertEdgeInternal(Function &Callee) {
79 if (Node *N = G->lookup(Callee))
80 return insertEdgeInternal(*N);
82 CalleeIndexMap.insert(std::make_pair(&Callee, Callees.size()));
83 Callees.push_back(&Callee);
86 void LazyCallGraph::Node::insertEdgeInternal(Node &CalleeN) {
87 CalleeIndexMap.insert(std::make_pair(&CalleeN.getFunction(), Callees.size()));
88 Callees.push_back(&CalleeN);
91 void LazyCallGraph::Node::removeEdgeInternal(Function &Callee) {
92 auto IndexMapI = CalleeIndexMap.find(&Callee);
93 assert(IndexMapI != CalleeIndexMap.end() &&
94 "Callee not in the callee set for this caller?");
96 Callees[IndexMapI->second] = nullptr;
97 CalleeIndexMap.erase(IndexMapI);
100 LazyCallGraph::LazyCallGraph(Module &M) : NextDFSNumber(0) {
101 DEBUG(dbgs() << "Building CG for module: " << M.getModuleIdentifier()
103 for (Function &F : M)
104 if (!F.isDeclaration() && !F.hasLocalLinkage())
105 if (EntryIndexMap.insert(std::make_pair(&F, EntryNodes.size())).second) {
106 DEBUG(dbgs() << " Adding '" << F.getName()
107 << "' to entry set of the graph.\n");
108 EntryNodes.push_back(&F);
111 // Now add entry nodes for functions reachable via initializers to globals.
112 SmallVector<Constant *, 16> Worklist;
113 SmallPtrSet<Constant *, 16> Visited;
114 for (GlobalVariable &GV : M.globals())
115 if (GV.hasInitializer())
116 if (Visited.insert(GV.getInitializer()).second)
117 Worklist.push_back(GV.getInitializer());
119 DEBUG(dbgs() << " Adding functions referenced by global initializers to the "
121 findCallees(Worklist, Visited, EntryNodes, EntryIndexMap);
123 for (auto &Entry : EntryNodes) {
124 assert(!Entry.isNull() &&
125 "We can't have removed edges before we finish the constructor!");
126 if (Function *F = Entry.dyn_cast<Function *>())
127 SCCEntryNodes.push_back(F);
129 SCCEntryNodes.push_back(&Entry.get<Node *>()->getFunction());
133 LazyCallGraph::LazyCallGraph(LazyCallGraph &&G)
134 : BPA(std::move(G.BPA)), NodeMap(std::move(G.NodeMap)),
135 EntryNodes(std::move(G.EntryNodes)),
136 EntryIndexMap(std::move(G.EntryIndexMap)), SCCBPA(std::move(G.SCCBPA)),
137 SCCMap(std::move(G.SCCMap)), LeafSCCs(std::move(G.LeafSCCs)),
138 DFSStack(std::move(G.DFSStack)),
139 SCCEntryNodes(std::move(G.SCCEntryNodes)),
140 NextDFSNumber(G.NextDFSNumber) {
144 LazyCallGraph &LazyCallGraph::operator=(LazyCallGraph &&G) {
145 BPA = std::move(G.BPA);
146 NodeMap = std::move(G.NodeMap);
147 EntryNodes = std::move(G.EntryNodes);
148 EntryIndexMap = std::move(G.EntryIndexMap);
149 SCCBPA = std::move(G.SCCBPA);
150 SCCMap = std::move(G.SCCMap);
151 LeafSCCs = std::move(G.LeafSCCs);
152 DFSStack = std::move(G.DFSStack);
153 SCCEntryNodes = std::move(G.SCCEntryNodes);
154 NextDFSNumber = G.NextDFSNumber;
159 void LazyCallGraph::SCC::insert(Node &N) {
160 N.DFSNumber = N.LowLink = -1;
162 G->SCCMap[&N] = this;
165 bool LazyCallGraph::SCC::isDescendantOf(const SCC &C) const {
166 // Walk up the parents of this SCC and verify that we eventually find C.
167 SmallVector<const SCC *, 4> AncestorWorklist;
168 AncestorWorklist.push_back(this);
170 const SCC *AncestorC = AncestorWorklist.pop_back_val();
171 if (AncestorC->isChildOf(C))
173 for (const SCC *ParentC : AncestorC->ParentSCCs)
174 AncestorWorklist.push_back(ParentC);
175 } while (!AncestorWorklist.empty());
180 void LazyCallGraph::SCC::insertIntraSCCEdge(Node &CallerN, Node &CalleeN) {
181 // First insert it into the caller.
182 CallerN.insertEdgeInternal(CalleeN);
184 assert(G->SCCMap.lookup(&CallerN) == this && "Caller must be in this SCC.");
185 assert(G->SCCMap.lookup(&CalleeN) == this && "Callee must be in this SCC.");
187 // Nothing changes about this SCC or any other.
190 void LazyCallGraph::SCC::insertOutgoingEdge(Node &CallerN, Node &CalleeN) {
191 // First insert it into the caller.
192 CallerN.insertEdgeInternal(CalleeN);
194 assert(G->SCCMap.lookup(&CallerN) == this && "Caller must be in this SCC.");
196 SCC &CalleeC = *G->SCCMap.lookup(&CalleeN);
197 assert(&CalleeC != this && "Callee must not be in this SCC.");
198 assert(CalleeC.isDescendantOf(*this) &&
199 "Callee must be a descendant of the Caller.");
201 // The only change required is to add this SCC to the parent set of the
203 CalleeC.ParentSCCs.insert(this);
206 SmallVector<LazyCallGraph::SCC *, 1>
207 LazyCallGraph::SCC::insertIncomingEdge(Node &CallerN, Node &CalleeN) {
208 // First insert it into the caller.
209 CallerN.insertEdgeInternal(CalleeN);
211 assert(G->SCCMap.lookup(&CalleeN) == this && "Callee must be in this SCC.");
213 SCC &CallerC = *G->SCCMap.lookup(&CallerN);
214 assert(&CallerC != this && "Caller must not be in this SCC.");
215 assert(CallerC.isDescendantOf(*this) &&
216 "Caller must be a descendant of the Callee.");
218 // The algorithm we use for merging SCCs based on the cycle introduced here
219 // is to walk the SCC inverted DAG formed by the parent SCC sets. The inverse
220 // graph has the same cycle properties as the actual DAG of the SCCs, and
221 // when forming SCCs lazily by a DFS, the bottom of the graph won't exist in
222 // many cases which should prune the search space.
224 // FIXME: We can get this pruning behavior even after the incremental SCC
225 // formation by leaving behind (conservative) DFS numberings in the nodes,
226 // and pruning the search with them. These would need to be cleverly updated
227 // during the removal of intra-SCC edges, but could be preserved
230 // The set of SCCs that are connected to the caller, and thus will
231 // participate in the merged connected component.
232 SmallPtrSet<SCC *, 8> ConnectedSCCs;
233 ConnectedSCCs.insert(this);
234 ConnectedSCCs.insert(&CallerC);
236 // We build up a DFS stack of the parents chains.
237 SmallVector<std::pair<SCC *, SCC::parent_iterator>, 8> DFSSCCs;
238 SmallPtrSet<SCC *, 8> VisitedSCCs;
239 int ConnectedDepth = -1;
241 parent_iterator I = parent_begin(), E = parent_end();
244 SCC &ParentSCC = *I++;
246 // If we have already processed this parent SCC, skip it, and remember
247 // whether it was connected so we don't have to check the rest of the
248 // stack. This also handles when we reach a child of the 'this' SCC (the
249 // callee) which terminates the search.
250 if (ConnectedSCCs.count(&ParentSCC)) {
251 ConnectedDepth = std::max<int>(ConnectedDepth, DFSSCCs.size());
254 if (VisitedSCCs.count(&ParentSCC))
257 // We fully explore the depth-first space, adding nodes to the connected
258 // set only as we pop them off, so "recurse" by rotating to the parent.
259 DFSSCCs.push_back(std::make_pair(C, I));
261 I = ParentSCC.parent_begin();
262 E = ParentSCC.parent_end();
265 // If we've found a connection anywhere below this point on the stack (and
266 // thus up the parent graph from the caller), the current node needs to be
267 // added to the connected set now that we've processed all of its parents.
268 if ((int)DFSSCCs.size() == ConnectedDepth) {
269 --ConnectedDepth; // We're finished with this connection.
270 ConnectedSCCs.insert(C);
272 // Otherwise remember that its parents don't ever connect.
273 assert(ConnectedDepth < (int)DFSSCCs.size() &&
274 "Cannot have a connected depth greater than the DFS depth!");
275 VisitedSCCs.insert(C);
279 break; // We've walked all the parents of the caller transitively.
281 // Pop off the prior node and position to unwind the depth first recursion.
282 std::tie(C, I) = DFSSCCs.pop_back_val();
286 // Now that we have identified all of the SCCs which need to be merged into
287 // a connected set with the inserted edge, merge all of them into this SCC.
288 // FIXME: This operation currently creates ordering stability problems
289 // because we don't use stably ordered containers for the parent SCCs or the
291 unsigned NewNodeBeginIdx = Nodes.size();
292 for (SCC *C : ConnectedSCCs) {
295 for (SCC *ParentC : C->ParentSCCs)
296 if (!ConnectedSCCs.count(ParentC))
297 ParentSCCs.insert(ParentC);
298 C->ParentSCCs.clear();
301 for (Node &ChildN : *N) {
302 SCC &ChildC = *G->SCCMap.lookup(&ChildN);
304 ChildC.ParentSCCs.erase(C);
311 for (auto I = Nodes.begin() + NewNodeBeginIdx, E = Nodes.end(); I != E; ++I)
312 for (Node &ChildN : **I) {
313 SCC &ChildC = *G->SCCMap.lookup(&ChildN);
315 ChildC.ParentSCCs.insert(this);
318 // We return the list of SCCs which were merged so that callers can
319 // invalidate any data they have associated with those SCCs. Note that these
320 // SCCs are no longer in an interesting state (they are totally empty) but
321 // the pointers will remain stable for the life of the graph itself.
322 return SmallVector<SCC *, 1>(ConnectedSCCs.begin(), ConnectedSCCs.end());
325 void LazyCallGraph::SCC::removeInterSCCEdge(Node &CallerN, Node &CalleeN) {
326 // First remove it from the node.
327 CallerN.removeEdgeInternal(CalleeN.getFunction());
329 assert(G->SCCMap.lookup(&CallerN) == this &&
330 "The caller must be a member of this SCC.");
332 SCC &CalleeC = *G->SCCMap.lookup(&CalleeN);
333 assert(&CalleeC != this &&
334 "This API only supports the rmoval of inter-SCC edges.");
336 assert(std::find(G->LeafSCCs.begin(), G->LeafSCCs.end(), this) ==
338 "Cannot have a leaf SCC caller with a different SCC callee.");
340 bool HasOtherCallToCalleeC = false;
341 bool HasOtherCallOutsideSCC = false;
342 for (Node *N : *this) {
343 for (Node &OtherCalleeN : *N) {
344 SCC &OtherCalleeC = *G->SCCMap.lookup(&OtherCalleeN);
345 if (&OtherCalleeC == &CalleeC) {
346 HasOtherCallToCalleeC = true;
349 if (&OtherCalleeC != this)
350 HasOtherCallOutsideSCC = true;
352 if (HasOtherCallToCalleeC)
355 // Because the SCCs form a DAG, deleting such an edge cannot change the set
356 // of SCCs in the graph. However, it may cut an edge of the SCC DAG, making
357 // the caller no longer a parent of the callee. Walk the other call edges
358 // in the caller to tell.
359 if (!HasOtherCallToCalleeC) {
360 bool Removed = CalleeC.ParentSCCs.erase(this);
363 "Did not find the caller SCC in the callee SCC's parent list!");
365 // It may orphan an SCC if it is the last edge reaching it, but that does
366 // not violate any invariants of the graph.
367 if (CalleeC.ParentSCCs.empty())
368 DEBUG(dbgs() << "LCG: Update removing " << CallerN.getFunction().getName()
369 << " -> " << CalleeN.getFunction().getName()
370 << " edge orphaned the callee's SCC!\n");
373 // It may make the Caller SCC a leaf SCC.
374 if (!HasOtherCallOutsideSCC)
375 G->LeafSCCs.push_back(this);
378 void LazyCallGraph::SCC::internalDFS(
379 SmallVectorImpl<std::pair<Node *, Node::iterator>> &DFSStack,
380 SmallVectorImpl<Node *> &PendingSCCStack, Node *N,
381 SmallVectorImpl<SCC *> &ResultSCCs) {
382 Node::iterator I = N->begin();
383 N->LowLink = N->DFSNumber = 1;
384 int NextDFSNumber = 2;
386 assert(N->DFSNumber != 0 && "We should always assign a DFS number "
387 "before processing a node.");
389 // We simulate recursion by popping out of the nested loop and continuing.
390 Node::iterator E = N->end();
393 if (SCC *ChildSCC = G->SCCMap.lookup(&ChildN)) {
394 // Check if we have reached a node in the new (known connected) set of
395 // this SCC. If so, the entire stack is necessarily in that set and we
397 if (ChildSCC == this) {
399 while (!PendingSCCStack.empty())
400 insert(*PendingSCCStack.pop_back_val());
401 while (!DFSStack.empty())
402 insert(*DFSStack.pop_back_val().first);
406 // If this child isn't currently in this SCC, no need to process it.
407 // However, we do need to remove this SCC from its SCC's parent set.
408 ChildSCC->ParentSCCs.erase(this);
413 if (ChildN.DFSNumber == 0) {
414 // Mark that we should start at this child when next this node is the
415 // top of the stack. We don't start at the next child to ensure this
416 // child's lowlink is reflected.
417 DFSStack.push_back(std::make_pair(N, I));
419 // Continue, resetting to the child node.
420 ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
427 // Track the lowest link of the children, if any are still in the stack.
428 // Any child not on the stack will have a LowLink of -1.
429 assert(ChildN.LowLink != 0 &&
430 "Low-link must not be zero with a non-zero DFS number.");
431 if (ChildN.LowLink >= 0 && ChildN.LowLink < N->LowLink)
432 N->LowLink = ChildN.LowLink;
436 if (N->LowLink == N->DFSNumber) {
437 ResultSCCs.push_back(G->formSCC(N, PendingSCCStack));
438 if (DFSStack.empty())
441 // At this point we know that N cannot ever be an SCC root. Its low-link
442 // is not its dfs-number, and we've processed all of its children. It is
443 // just sitting here waiting until some node further down the stack gets
444 // low-link == dfs-number and pops it off as well. Move it to the pending
445 // stack which is pulled into the next SCC to be formed.
446 PendingSCCStack.push_back(N);
448 assert(!DFSStack.empty() && "We shouldn't have an empty stack!");
451 N = DFSStack.back().first;
452 I = DFSStack.back().second;
457 SmallVector<LazyCallGraph::SCC *, 1>
458 LazyCallGraph::SCC::removeIntraSCCEdge(Node &CallerN, Node &CalleeN) {
459 // First remove it from the node.
460 CallerN.removeEdgeInternal(CalleeN.getFunction());
462 // We return a list of the resulting *new* SCCs in postorder.
463 SmallVector<SCC *, 1> ResultSCCs;
465 // Direct recursion doesn't impact the SCC graph at all.
466 if (&CallerN == &CalleeN)
469 // The worklist is every node in the original SCC.
470 SmallVector<Node *, 1> Worklist;
471 Worklist.swap(Nodes);
472 for (Node *N : Worklist) {
473 // The nodes formerly in this SCC are no longer in any SCC.
478 assert(Worklist.size() > 1 && "We have to have at least two nodes to have an "
479 "edge between them that is within the SCC.");
481 // The callee can already reach every node in this SCC (by definition). It is
482 // the only node we know will stay inside this SCC. Everything which
483 // transitively reaches Callee will also remain in the SCC. To model this we
484 // incrementally add any chain of nodes which reaches something in the new
485 // node set to the new node set. This short circuits one side of the Tarjan's
489 // We're going to do a full mini-Tarjan's walk using a local stack here.
490 SmallVector<std::pair<Node *, Node::iterator>, 4> DFSStack;
491 SmallVector<Node *, 4> PendingSCCStack;
493 Node *N = Worklist.pop_back_val();
494 if (N->DFSNumber == 0)
495 internalDFS(DFSStack, PendingSCCStack, N, ResultSCCs);
497 assert(DFSStack.empty() && "Didn't flush the entire DFS stack!");
498 assert(PendingSCCStack.empty() && "Didn't flush all pending SCC nodes!");
499 } while (!Worklist.empty());
501 // Now we need to reconnect the current SCC to the graph.
502 bool IsLeafSCC = true;
503 for (Node *N : Nodes) {
504 for (Node &ChildN : *N) {
505 SCC &ChildSCC = *G->SCCMap.lookup(&ChildN);
506 if (&ChildSCC == this)
508 ChildSCC.ParentSCCs.insert(this);
513 if (!ResultSCCs.empty())
514 assert(!IsLeafSCC && "This SCC cannot be a leaf as we have split out new "
515 "SCCs by removing this edge.");
516 if (!std::any_of(G->LeafSCCs.begin(), G->LeafSCCs.end(),
517 [&](SCC *C) { return C == this; }))
518 assert(!IsLeafSCC && "This SCC cannot be a leaf as it already had child "
519 "SCCs before we removed this edge.");
521 // If this SCC stopped being a leaf through this edge removal, remove it from
522 // the leaf SCC list.
523 if (!IsLeafSCC && !ResultSCCs.empty())
524 G->LeafSCCs.erase(std::remove(G->LeafSCCs.begin(), G->LeafSCCs.end(), this),
527 // Return the new list of SCCs.
531 void LazyCallGraph::insertEdge(Node &CallerN, Function &Callee) {
532 assert(SCCMap.empty() && DFSStack.empty() &&
533 "This method cannot be called after SCCs have been formed!");
535 return CallerN.insertEdgeInternal(Callee);
538 void LazyCallGraph::removeEdge(Node &CallerN, Function &Callee) {
539 assert(SCCMap.empty() && DFSStack.empty() &&
540 "This method cannot be called after SCCs have been formed!");
542 return CallerN.removeEdgeInternal(Callee);
545 LazyCallGraph::Node &LazyCallGraph::insertInto(Function &F, Node *&MappedN) {
546 return *new (MappedN = BPA.Allocate()) Node(*this, F);
549 void LazyCallGraph::updateGraphPtrs() {
550 // Process all nodes updating the graph pointers.
552 SmallVector<Node *, 16> Worklist;
553 for (auto &Entry : EntryNodes)
554 if (Node *EntryN = Entry.dyn_cast<Node *>())
555 Worklist.push_back(EntryN);
557 while (!Worklist.empty()) {
558 Node *N = Worklist.pop_back_val();
560 for (auto &Callee : N->Callees)
561 if (!Callee.isNull())
562 if (Node *CalleeN = Callee.dyn_cast<Node *>())
563 Worklist.push_back(CalleeN);
567 // Process all SCCs updating the graph pointers.
569 SmallVector<SCC *, 16> Worklist(LeafSCCs.begin(), LeafSCCs.end());
571 while (!Worklist.empty()) {
572 SCC *C = Worklist.pop_back_val();
574 Worklist.insert(Worklist.end(), C->ParentSCCs.begin(),
575 C->ParentSCCs.end());
580 LazyCallGraph::SCC *LazyCallGraph::formSCC(Node *RootN,
581 SmallVectorImpl<Node *> &NodeStack) {
582 // The tail of the stack is the new SCC. Allocate the SCC and pop the stack
584 SCC *NewSCC = new (SCCBPA.Allocate()) SCC(*this);
586 while (!NodeStack.empty() && NodeStack.back()->DFSNumber > RootN->DFSNumber) {
587 assert(NodeStack.back()->LowLink >= RootN->LowLink &&
588 "We cannot have a low link in an SCC lower than its root on the "
590 NewSCC->insert(*NodeStack.pop_back_val());
592 NewSCC->insert(*RootN);
594 // A final pass over all edges in the SCC (this remains linear as we only
595 // do this once when we build the SCC) to connect it to the parent sets of
597 bool IsLeafSCC = true;
598 for (Node *SCCN : NewSCC->Nodes)
599 for (Node &SCCChildN : *SCCN) {
600 SCC &ChildSCC = *SCCMap.lookup(&SCCChildN);
601 if (&ChildSCC == NewSCC)
603 ChildSCC.ParentSCCs.insert(NewSCC);
607 // For the SCCs where we fine no child SCCs, add them to the leaf list.
609 LeafSCCs.push_back(NewSCC);
614 LazyCallGraph::SCC *LazyCallGraph::getNextSCCInPostOrder() {
617 if (!DFSStack.empty()) {
618 N = DFSStack.back().first;
619 I = DFSStack.back().second;
622 // If we've handled all candidate entry nodes to the SCC forest, we're done.
624 if (SCCEntryNodes.empty())
627 N = &get(*SCCEntryNodes.pop_back_val());
628 } while (N->DFSNumber != 0);
630 N->LowLink = N->DFSNumber = 1;
635 assert(N->DFSNumber != 0 && "We should always assign a DFS number "
636 "before placing a node onto the stack.");
638 Node::iterator E = N->end();
641 if (ChildN.DFSNumber == 0) {
642 // Mark that we should start at this child when next this node is the
643 // top of the stack. We don't start at the next child to ensure this
644 // child's lowlink is reflected.
645 DFSStack.push_back(std::make_pair(N, N->begin()));
647 // Recurse onto this node via a tail call.
648 assert(!SCCMap.count(&ChildN) &&
649 "Found a node with 0 DFS number but already in an SCC!");
650 ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
657 // Track the lowest link of the children, if any are still in the stack.
658 assert(ChildN.LowLink != 0 &&
659 "Low-link must not be zero with a non-zero DFS number.");
660 if (ChildN.LowLink >= 0 && ChildN.LowLink < N->LowLink)
661 N->LowLink = ChildN.LowLink;
665 if (N->LowLink == N->DFSNumber)
666 // Form the new SCC out of the top of the DFS stack.
667 return formSCC(N, PendingSCCStack);
669 // At this point we know that N cannot ever be an SCC root. Its low-link
670 // is not its dfs-number, and we've processed all of its children. It is
671 // just sitting here waiting until some node further down the stack gets
672 // low-link == dfs-number and pops it off as well. Move it to the pending
673 // stack which is pulled into the next SCC to be formed.
674 PendingSCCStack.push_back(N);
676 assert(!DFSStack.empty() && "We never found a viable root!");
677 N = DFSStack.back().first;
678 I = DFSStack.back().second;
683 char LazyCallGraphAnalysis::PassID;
685 LazyCallGraphPrinterPass::LazyCallGraphPrinterPass(raw_ostream &OS) : OS(OS) {}
687 static void printNodes(raw_ostream &OS, LazyCallGraph::Node &N,
688 SmallPtrSetImpl<LazyCallGraph::Node *> &Printed) {
689 // Recurse depth first through the nodes.
690 for (LazyCallGraph::Node &ChildN : N)
691 if (Printed.insert(&ChildN).second)
692 printNodes(OS, ChildN, Printed);
694 OS << " Call edges in function: " << N.getFunction().getName() << "\n";
695 for (LazyCallGraph::iterator I = N.begin(), E = N.end(); I != E; ++I)
696 OS << " -> " << I->getFunction().getName() << "\n";
701 static void printSCC(raw_ostream &OS, LazyCallGraph::SCC &SCC) {
702 ptrdiff_t SCCSize = std::distance(SCC.begin(), SCC.end());
703 OS << " SCC with " << SCCSize << " functions:\n";
705 for (LazyCallGraph::Node *N : SCC)
706 OS << " " << N->getFunction().getName() << "\n";
711 PreservedAnalyses LazyCallGraphPrinterPass::run(Module &M,
712 ModuleAnalysisManager *AM) {
713 LazyCallGraph &G = AM->getResult<LazyCallGraphAnalysis>(M);
715 OS << "Printing the call graph for module: " << M.getModuleIdentifier()
718 SmallPtrSet<LazyCallGraph::Node *, 16> Printed;
719 for (LazyCallGraph::Node &N : G)
720 if (Printed.insert(&N).second)
721 printNodes(OS, N, Printed);
723 for (LazyCallGraph::SCC &SCC : G.postorder_sccs())
726 return PreservedAnalyses::all();