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)))
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))
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()))
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 callee.
202 CalleeC.ParentSCCs.insert(this);
205 void LazyCallGraph::SCC::removeInterSCCEdge(Node &CallerN, Node &CalleeN) {
206 // First remove it from the node.
207 CallerN.removeEdgeInternal(CalleeN.getFunction());
209 assert(G->SCCMap.lookup(&CallerN) == this &&
210 "The caller must be a member of this SCC.");
212 SCC &CalleeC = *G->SCCMap.lookup(&CalleeN);
213 assert(&CalleeC != this &&
214 "This API only supports the rmoval of inter-SCC edges.");
216 assert(std::find(G->LeafSCCs.begin(), G->LeafSCCs.end(), this) ==
218 "Cannot have a leaf SCC caller with a different SCC callee.");
220 bool HasOtherCallToCalleeC = false;
221 bool HasOtherCallOutsideSCC = false;
222 for (Node *N : *this) {
223 for (Node &OtherCalleeN : *N) {
224 SCC &OtherCalleeC = *G->SCCMap.lookup(&OtherCalleeN);
225 if (&OtherCalleeC == &CalleeC) {
226 HasOtherCallToCalleeC = true;
229 if (&OtherCalleeC != this)
230 HasOtherCallOutsideSCC = true;
232 if (HasOtherCallToCalleeC)
235 // Because the SCCs form a DAG, deleting such an edge cannot change the set
236 // of SCCs in the graph. However, it may cut an edge of the SCC DAG, making
237 // the caller no longer a parent of the callee. Walk the other call edges
238 // in the caller to tell.
239 if (!HasOtherCallToCalleeC) {
240 bool Removed = CalleeC.ParentSCCs.erase(this);
243 "Did not find the caller SCC in the callee SCC's parent list!");
245 // It may orphan an SCC if it is the last edge reaching it, but that does
246 // not violate any invariants of the graph.
247 if (CalleeC.ParentSCCs.empty())
248 DEBUG(dbgs() << "LCG: Update removing " << CallerN.getFunction().getName()
249 << " -> " << CalleeN.getFunction().getName()
250 << " edge orphaned the callee's SCC!\n");
253 // It may make the Caller SCC a leaf SCC.
254 if (!HasOtherCallOutsideSCC)
255 G->LeafSCCs.push_back(this);
258 void LazyCallGraph::SCC::internalDFS(
259 SmallVectorImpl<std::pair<Node *, Node::iterator>> &DFSStack,
260 SmallVectorImpl<Node *> &PendingSCCStack, Node *N,
261 SmallVectorImpl<SCC *> &ResultSCCs) {
262 Node::iterator I = N->begin();
263 N->LowLink = N->DFSNumber = 1;
264 int NextDFSNumber = 2;
266 assert(N->DFSNumber != 0 && "We should always assign a DFS number "
267 "before processing a node.");
269 // We simulate recursion by popping out of the nested loop and continuing.
270 Node::iterator E = N->end();
273 if (SCC *ChildSCC = G->SCCMap.lookup(&ChildN)) {
274 // Check if we have reached a node in the new (known connected) set of
275 // this SCC. If so, the entire stack is necessarily in that set and we
277 if (ChildSCC == this) {
279 while (!PendingSCCStack.empty())
280 insert(*PendingSCCStack.pop_back_val());
281 while (!DFSStack.empty())
282 insert(*DFSStack.pop_back_val().first);
286 // If this child isn't currently in this SCC, no need to process it.
287 // However, we do need to remove this SCC from its SCC's parent set.
288 ChildSCC->ParentSCCs.erase(this);
293 if (ChildN.DFSNumber == 0) {
294 // Mark that we should start at this child when next this node is the
295 // top of the stack. We don't start at the next child to ensure this
296 // child's lowlink is reflected.
297 DFSStack.push_back(std::make_pair(N, I));
299 // Continue, resetting to the child node.
300 ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
307 // Track the lowest link of the childen, if any are still in the stack.
308 // Any child not on the stack will have a LowLink of -1.
309 assert(ChildN.LowLink != 0 &&
310 "Low-link must not be zero with a non-zero DFS number.");
311 if (ChildN.LowLink >= 0 && ChildN.LowLink < N->LowLink)
312 N->LowLink = ChildN.LowLink;
316 if (N->LowLink == N->DFSNumber) {
317 ResultSCCs.push_back(G->formSCC(N, PendingSCCStack));
318 if (DFSStack.empty())
321 // At this point we know that N cannot ever be an SCC root. Its low-link
322 // is not its dfs-number, and we've processed all of its children. It is
323 // just sitting here waiting until some node further down the stack gets
324 // low-link == dfs-number and pops it off as well. Move it to the pending
325 // stack which is pulled into the next SCC to be formed.
326 PendingSCCStack.push_back(N);
328 assert(!DFSStack.empty() && "We shouldn't have an empty stack!");
331 N = DFSStack.back().first;
332 I = DFSStack.back().second;
337 SmallVector<LazyCallGraph::SCC *, 1>
338 LazyCallGraph::SCC::removeIntraSCCEdge(Node &CallerN,
340 // First remove it from the node.
341 CallerN.removeEdgeInternal(CalleeN.getFunction());
343 // We return a list of the resulting *new* SCCs in postorder.
344 SmallVector<SCC *, 1> ResultSCCs;
346 // Direct recursion doesn't impact the SCC graph at all.
347 if (&CallerN == &CalleeN)
350 // The worklist is every node in the original SCC.
351 SmallVector<Node *, 1> Worklist;
352 Worklist.swap(Nodes);
353 for (Node *N : Worklist) {
354 // The nodes formerly in this SCC are no longer in any SCC.
359 assert(Worklist.size() > 1 && "We have to have at least two nodes to have an "
360 "edge between them that is within the SCC.");
362 // The callee can already reach every node in this SCC (by definition). It is
363 // the only node we know will stay inside this SCC. Everything which
364 // transitively reaches Callee will also remain in the SCC. To model this we
365 // incrementally add any chain of nodes which reaches something in the new
366 // node set to the new node set. This short circuits one side of the Tarjan's
370 // We're going to do a full mini-Tarjan's walk using a local stack here.
371 SmallVector<std::pair<Node *, Node::iterator>, 4> DFSStack;
372 SmallVector<Node *, 4> PendingSCCStack;
374 Node *N = Worklist.pop_back_val();
375 if (N->DFSNumber == 0)
376 internalDFS(DFSStack, PendingSCCStack, N, ResultSCCs);
378 assert(DFSStack.empty() && "Didn't flush the entire DFS stack!");
379 assert(PendingSCCStack.empty() && "Didn't flush all pending SCC nodes!");
380 } while (!Worklist.empty());
382 // Now we need to reconnect the current SCC to the graph.
383 bool IsLeafSCC = true;
384 for (Node *N : Nodes) {
385 for (Node &ChildN : *N) {
386 SCC &ChildSCC = *G->SCCMap.lookup(&ChildN);
387 if (&ChildSCC == this)
389 ChildSCC.ParentSCCs.insert(this);
394 if (!ResultSCCs.empty())
395 assert(!IsLeafSCC && "This SCC cannot be a leaf as we have split out new "
396 "SCCs by removing this edge.");
397 if (!std::any_of(G->LeafSCCs.begin(), G->LeafSCCs.end(),
398 [&](SCC *C) { return C == this; }))
399 assert(!IsLeafSCC && "This SCC cannot be a leaf as it already had child "
400 "SCCs before we removed this edge.");
402 // If this SCC stopped being a leaf through this edge removal, remove it from
403 // the leaf SCC list.
404 if (!IsLeafSCC && !ResultSCCs.empty())
405 G->LeafSCCs.erase(std::remove(G->LeafSCCs.begin(), G->LeafSCCs.end(), this),
408 // Return the new list of SCCs.
412 void LazyCallGraph::insertEdge(Node &CallerN, Function &Callee) {
413 assert(SCCMap.empty() && DFSStack.empty() &&
414 "This method cannot be called after SCCs have been formed!");
416 return CallerN.insertEdgeInternal(Callee);
419 void LazyCallGraph::removeEdge(Node &CallerN, Function &Callee) {
420 assert(SCCMap.empty() && DFSStack.empty() &&
421 "This method cannot be called after SCCs have been formed!");
423 return CallerN.removeEdgeInternal(Callee);
426 LazyCallGraph::Node &LazyCallGraph::insertInto(Function &F, Node *&MappedN) {
427 return *new (MappedN = BPA.Allocate()) Node(*this, F);
430 void LazyCallGraph::updateGraphPtrs() {
431 // Process all nodes updating the graph pointers.
433 SmallVector<Node *, 16> Worklist;
434 for (auto &Entry : EntryNodes)
435 if (Node *EntryN = Entry.dyn_cast<Node *>())
436 Worklist.push_back(EntryN);
438 while (!Worklist.empty()) {
439 Node *N = Worklist.pop_back_val();
441 for (auto &Callee : N->Callees)
442 if (!Callee.isNull())
443 if (Node *CalleeN = Callee.dyn_cast<Node *>())
444 Worklist.push_back(CalleeN);
448 // Process all SCCs updating the graph pointers.
450 SmallVector<SCC *, 16> Worklist(LeafSCCs.begin(), LeafSCCs.end());
452 while (!Worklist.empty()) {
453 SCC *C = Worklist.pop_back_val();
455 Worklist.insert(Worklist.end(), C->ParentSCCs.begin(),
456 C->ParentSCCs.end());
461 LazyCallGraph::SCC *LazyCallGraph::formSCC(Node *RootN,
462 SmallVectorImpl<Node *> &NodeStack) {
463 // The tail of the stack is the new SCC. Allocate the SCC and pop the stack
465 SCC *NewSCC = new (SCCBPA.Allocate()) SCC(*this);
467 while (!NodeStack.empty() && NodeStack.back()->DFSNumber > RootN->DFSNumber) {
468 assert(NodeStack.back()->LowLink >= RootN->LowLink &&
469 "We cannot have a low link in an SCC lower than its root on the "
471 NewSCC->insert(*NodeStack.pop_back_val());
473 NewSCC->insert(*RootN);
475 // A final pass over all edges in the SCC (this remains linear as we only
476 // do this once when we build the SCC) to connect it to the parent sets of
478 bool IsLeafSCC = true;
479 for (Node *SCCN : NewSCC->Nodes)
480 for (Node &SCCChildN : *SCCN) {
481 SCC &ChildSCC = *SCCMap.lookup(&SCCChildN);
482 if (&ChildSCC == NewSCC)
484 ChildSCC.ParentSCCs.insert(NewSCC);
488 // For the SCCs where we fine no child SCCs, add them to the leaf list.
490 LeafSCCs.push_back(NewSCC);
495 LazyCallGraph::SCC *LazyCallGraph::getNextSCCInPostOrder() {
498 if (!DFSStack.empty()) {
499 N = DFSStack.back().first;
500 I = DFSStack.back().second;
503 // If we've handled all candidate entry nodes to the SCC forest, we're done.
505 if (SCCEntryNodes.empty())
508 N = &get(*SCCEntryNodes.pop_back_val());
509 } while (N->DFSNumber != 0);
511 N->LowLink = N->DFSNumber = 1;
516 assert(N->DFSNumber != 0 && "We should always assign a DFS number "
517 "before placing a node onto the stack.");
519 Node::iterator E = N->end();
522 if (ChildN.DFSNumber == 0) {
523 // Mark that we should start at this child when next this node is the
524 // top of the stack. We don't start at the next child to ensure this
525 // child's lowlink is reflected.
526 DFSStack.push_back(std::make_pair(N, N->begin()));
528 // Recurse onto this node via a tail call.
529 assert(!SCCMap.count(&ChildN) &&
530 "Found a node with 0 DFS number but already in an SCC!");
531 ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
538 // Track the lowest link of the childen, if any are still in the stack.
539 assert(ChildN.LowLink != 0 &&
540 "Low-link must not be zero with a non-zero DFS number.");
541 if (ChildN.LowLink >= 0 && ChildN.LowLink < N->LowLink)
542 N->LowLink = ChildN.LowLink;
546 if (N->LowLink == N->DFSNumber)
547 // Form the new SCC out of the top of the DFS stack.
548 return formSCC(N, PendingSCCStack);
550 // At this point we know that N cannot ever be an SCC root. Its low-link
551 // is not its dfs-number, and we've processed all of its children. It is
552 // just sitting here waiting until some node further down the stack gets
553 // low-link == dfs-number and pops it off as well. Move it to the pending
554 // stack which is pulled into the next SCC to be formed.
555 PendingSCCStack.push_back(N);
557 assert(!DFSStack.empty() && "We never found a viable root!");
558 N = DFSStack.back().first;
559 I = DFSStack.back().second;
564 char LazyCallGraphAnalysis::PassID;
566 LazyCallGraphPrinterPass::LazyCallGraphPrinterPass(raw_ostream &OS) : OS(OS) {}
568 static void printNodes(raw_ostream &OS, LazyCallGraph::Node &N,
569 SmallPtrSetImpl<LazyCallGraph::Node *> &Printed) {
570 // Recurse depth first through the nodes.
571 for (LazyCallGraph::Node &ChildN : N)
572 if (Printed.insert(&ChildN))
573 printNodes(OS, ChildN, Printed);
575 OS << " Call edges in function: " << N.getFunction().getName() << "\n";
576 for (LazyCallGraph::iterator I = N.begin(), E = N.end(); I != E; ++I)
577 OS << " -> " << I->getFunction().getName() << "\n";
582 static void printSCC(raw_ostream &OS, LazyCallGraph::SCC &SCC) {
583 ptrdiff_t SCCSize = std::distance(SCC.begin(), SCC.end());
584 OS << " SCC with " << SCCSize << " functions:\n";
586 for (LazyCallGraph::Node *N : SCC)
587 OS << " " << N->getFunction().getName() << "\n";
592 PreservedAnalyses LazyCallGraphPrinterPass::run(Module *M,
593 ModuleAnalysisManager *AM) {
594 LazyCallGraph &G = AM->getResult<LazyCallGraphAnalysis>(M);
596 OS << "Printing the call graph for module: " << M->getModuleIdentifier()
599 SmallPtrSet<LazyCallGraph::Node *, 16> Printed;
600 for (LazyCallGraph::Node &N : G)
601 if (Printed.insert(&N))
602 printNodes(OS, N, Printed);
604 for (LazyCallGraph::SCC &SCC : G.postorder_sccs())
607 return PreservedAnalyses::all();