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 LazyCallGraph::LazyCallGraph(Module &M) : NextDFSNumber(0) {
79 DEBUG(dbgs() << "Building CG for module: " << M.getModuleIdentifier()
82 if (!F.isDeclaration() && !F.hasLocalLinkage())
83 if (EntryIndexMap.insert(std::make_pair(&F, EntryNodes.size())).second) {
84 DEBUG(dbgs() << " Adding '" << F.getName()
85 << "' to entry set of the graph.\n");
86 EntryNodes.push_back(&F);
89 // Now add entry nodes for functions reachable via initializers to globals.
90 SmallVector<Constant *, 16> Worklist;
91 SmallPtrSet<Constant *, 16> Visited;
92 for (GlobalVariable &GV : M.globals())
93 if (GV.hasInitializer())
94 if (Visited.insert(GV.getInitializer()))
95 Worklist.push_back(GV.getInitializer());
97 DEBUG(dbgs() << " Adding functions referenced by global initializers to the "
99 findCallees(Worklist, Visited, EntryNodes, EntryIndexMap);
101 for (auto &Entry : EntryNodes)
102 if (Function *F = Entry.dyn_cast<Function *>())
103 SCCEntryNodes.insert(F);
105 SCCEntryNodes.insert(&Entry.get<Node *>()->getFunction());
108 LazyCallGraph::LazyCallGraph(LazyCallGraph &&G)
109 : BPA(std::move(G.BPA)), NodeMap(std::move(G.NodeMap)),
110 EntryNodes(std::move(G.EntryNodes)),
111 EntryIndexMap(std::move(G.EntryIndexMap)), SCCBPA(std::move(G.SCCBPA)),
112 SCCMap(std::move(G.SCCMap)), LeafSCCs(std::move(G.LeafSCCs)),
113 DFSStack(std::move(G.DFSStack)),
114 SCCEntryNodes(std::move(G.SCCEntryNodes)),
115 NextDFSNumber(G.NextDFSNumber) {
119 LazyCallGraph &LazyCallGraph::operator=(LazyCallGraph &&G) {
120 BPA = std::move(G.BPA);
121 NodeMap = std::move(G.NodeMap);
122 EntryNodes = std::move(G.EntryNodes);
123 EntryIndexMap = std::move(G.EntryIndexMap);
124 SCCBPA = std::move(G.SCCBPA);
125 SCCMap = std::move(G.SCCMap);
126 LeafSCCs = std::move(G.LeafSCCs);
127 DFSStack = std::move(G.DFSStack);
128 SCCEntryNodes = std::move(G.SCCEntryNodes);
129 NextDFSNumber = G.NextDFSNumber;
134 void LazyCallGraph::SCC::removeEdge(LazyCallGraph &G, Function &Caller,
135 Function &Callee, SCC &CalleeC) {
136 assert(std::find(G.LeafSCCs.begin(), G.LeafSCCs.end(), this) ==
138 "Cannot have a leaf SCC caller with a different SCC callee.");
140 bool HasOtherCallToCalleeC = false;
141 bool HasOtherCallOutsideSCC = false;
142 for (Node *N : *this) {
143 for (Node &Callee : *N) {
144 SCC &OtherCalleeC = *G.SCCMap.lookup(&Callee);
145 if (&OtherCalleeC == &CalleeC) {
146 HasOtherCallToCalleeC = true;
149 if (&OtherCalleeC != this)
150 HasOtherCallOutsideSCC = true;
152 if (HasOtherCallToCalleeC)
155 // Because the SCCs form a DAG, deleting such an edge cannot change the set
156 // of SCCs in the graph. However, it may cut an edge of the SCC DAG, making
157 // the caller no longer a parent of the callee. Walk the other call edges
158 // in the caller to tell.
159 if (!HasOtherCallToCalleeC) {
160 bool Removed = CalleeC.ParentSCCs.erase(this);
163 "Did not find the caller SCC in the callee SCC's parent list!");
165 // It may orphan an SCC if it is the last edge reaching it, but that does
166 // not violate any invariants of the graph.
167 if (CalleeC.ParentSCCs.empty())
168 DEBUG(dbgs() << "LCG: Update removing " << Caller.getName() << " -> "
169 << Callee.getName() << " edge orphaned the callee's SCC!\n");
172 // It may make the Caller SCC a leaf SCC.
173 if (!HasOtherCallOutsideSCC)
174 G.LeafSCCs.push_back(this);
177 SmallVector<LazyCallGraph::SCC *, 1>
178 LazyCallGraph::SCC::removeInternalEdge(LazyCallGraph &G, Node &Caller,
180 // We return a list of the resulting SCCs, where 'this' is always the first
182 SmallVector<SCC *, 1> ResultSCCs;
183 ResultSCCs.push_back(this);
185 // We're going to do a full mini-Tarjan's walk using a local stack here.
187 SmallVector<std::pair<Node *, Node::iterator>, 4> DFSStack;
188 SmallVector<Node *, 4> PendingSCCStack;
190 // The worklist is every node in the original SCC.
191 SmallVector<Node *, 1> Worklist;
192 Worklist.swap(Nodes);
193 for (Node *N : Worklist) {
194 // Clear these to 0 while we re-run Tarjan's over the SCC.
199 // The callee can already reach every node in this SCC (by definition). It is
200 // the only node we know will stay inside this SCC. Everything which
201 // transitively reaches Callee will also remain in the SCC. To model this we
202 // incrementally add any chain of nodes which reaches something in the new
203 // node set to the new node set. This short circuits one side of the Tarjan's
205 SmallSetVector<Node *, 1> NewNodes;
206 NewNodes.insert(&Callee);
209 if (DFSStack.empty()) {
210 // Clear off any nodes which have already been visited in the DFS.
211 while (!Worklist.empty() && Worklist.back()->DFSNumber != 0)
213 if (Worklist.empty())
215 Node *N = Worklist.pop_back_val();
216 N->LowLink = N->DFSNumber = 1;
218 DFSStack.push_back(std::make_pair(N, N->begin()));
219 assert(PendingSCCStack.empty() && "Cannot start a fresh DFS walk with "
220 "pending nodes from a prior walk.");
223 Node *N = DFSStack.back().first;
224 assert(N->DFSNumber != 0 && "We should always assign a DFS number "
225 "before placing a node onto the stack.");
227 // We simulate recursion by popping out of the nested loop and continuing.
228 bool Recurse = false;
229 for (auto I = DFSStack.back().second, E = N->end(); I != E; ++I) {
231 // If this child isn't currently in this SCC, no need to process it.
232 // However, we do need to remove this SCC from its SCC's parent set.
233 SCC &ChildSCC = *G.SCCMap.lookup(&ChildN);
234 if (&ChildSCC != this) {
235 ChildSCC.ParentSCCs.erase(this);
239 // Check if we have reached a node in the new (known connected) set. If
240 // so, the entire stack is necessarily in that set and we can re-start.
241 if (NewNodes.count(&ChildN)) {
242 while (!PendingSCCStack.empty())
243 NewNodes.insert(PendingSCCStack.pop_back_val());
244 while (!DFSStack.empty())
245 NewNodes.insert(DFSStack.pop_back_val().first);
250 if (ChildN.DFSNumber == 0) {
251 // Mark that we should start at this child when next this node is the
252 // top of the stack. We don't start at the next child to ensure this
253 // child's lowlink is reflected.
254 DFSStack.back().second = I;
256 // Recurse onto this node via a tail call.
257 ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
258 DFSStack.push_back(std::make_pair(&ChildN, ChildN.begin()));
263 // Track the lowest link of the childen, if any are still in the stack.
264 // Any child not on the stack will have a LowLink of -1.
265 assert(ChildN.LowLink != 0 &&
266 "Low-link must not be zero with a non-zero DFS number.");
267 if (ChildN.LowLink >= 0 && ChildN.LowLink < N->LowLink)
268 N->LowLink = ChildN.LowLink;
273 // No more children to process, pop it off the core DFS stack.
276 if (N->LowLink == N->DFSNumber) {
277 ResultSCCs.push_back(G.formSCC(N, PendingSCCStack));
281 assert(!DFSStack.empty() && "We shouldn't have an empty stack!");
283 // At this point we know that N cannot ever be an SCC root. Its low-link
284 // is not its dfs-number, and we've processed all of its children. It is
285 // just sitting here waiting until some node further down the stack gets
286 // low-link == dfs-number and pops it off as well. Move it to the pending
287 // stack which is pulled into the next SCC to be formed.
288 PendingSCCStack.push_back(N);
291 // Replace this SCC with the NewNodes we collected above.
292 // FIXME: Simplify this when the SCC's datastructure is just a list.
295 // Now we need to reconnect the current SCC to the graph.
296 bool IsLeafSCC = true;
297 for (Node *N : NewNodes) {
301 for (Node &ChildN : *N) {
302 if (NewNodes.count(&ChildN))
304 SCC &ChildSCC = *G.SCCMap.lookup(&ChildN);
305 ChildSCC.ParentSCCs.insert(this);
310 if (ResultSCCs.size() > 1)
311 assert(!IsLeafSCC && "This SCC cannot be a leaf as we have split out new "
312 "SCCs by removing this edge.");
313 if (!std::any_of(G.LeafSCCs.begin(), G.LeafSCCs.end(),
314 [&](SCC *C) { return C == this; }))
315 assert(!IsLeafSCC && "This SCC cannot be a leaf as it already had child "
316 "SCCs before we removed this edge.");
318 // If this SCC stopped being a leaf through this edge removal, remove it from
319 // the leaf SCC list.
320 if (!IsLeafSCC && ResultSCCs.size() > 1)
321 G.LeafSCCs.erase(std::remove(G.LeafSCCs.begin(), G.LeafSCCs.end(), this),
324 // Return the new list of SCCs.
328 void LazyCallGraph::removeEdge(Node &CallerN, Function &Callee) {
329 auto IndexMapI = CallerN.CalleeIndexMap.find(&Callee);
330 assert(IndexMapI != CallerN.CalleeIndexMap.end() &&
331 "Callee not in the callee set for the caller?");
333 Node *CalleeN = CallerN.Callees[IndexMapI->second].dyn_cast<Node *>();
334 CallerN.Callees.erase(CallerN.Callees.begin() + IndexMapI->second);
335 CallerN.CalleeIndexMap.erase(IndexMapI);
337 SCC *CallerC = SCCMap.lookup(&CallerN);
339 // We can only remove edges when the edge isn't actively participating in
340 // a DFS walk. Either it must have been popped into an SCC, or it must not
341 // yet have been reached by the DFS walk. Assert the latter here.
342 assert(std::all_of(DFSStack.begin(), DFSStack.end(),
343 [&](const std::pair<Node *, iterator> &StackEntry) {
344 return StackEntry.first != &CallerN;
346 "Found the caller on the DFSStack!");
350 assert(CalleeN && "If the caller is in an SCC, we have to have explored all "
351 "its transitively called functions.");
353 SCC *CalleeC = SCCMap.lookup(CalleeN);
355 "The caller has an SCC, and thus by necessity so does the callee.");
357 // The easy case is when they are different SCCs.
358 if (CallerC != CalleeC) {
359 CallerC->removeEdge(*this, CallerN.getFunction(), Callee, *CalleeC);
363 // The hard case is when we remove an edge within a SCC. This may cause new
364 // SCCs to need to be added to the graph.
365 CallerC->removeInternalEdge(*this, CallerN, *CalleeN);
368 LazyCallGraph::Node &LazyCallGraph::insertInto(Function &F, Node *&MappedN) {
369 return *new (MappedN = BPA.Allocate()) Node(*this, F);
372 void LazyCallGraph::updateGraphPtrs() {
373 // Process all nodes updating the graph pointers.
374 SmallVector<Node *, 16> Worklist;
375 for (auto &Entry : EntryNodes)
376 if (Node *EntryN = Entry.dyn_cast<Node *>())
377 Worklist.push_back(EntryN);
379 while (!Worklist.empty()) {
380 Node *N = Worklist.pop_back_val();
382 for (auto &Callee : N->Callees)
383 if (Node *CalleeN = Callee.dyn_cast<Node *>())
384 Worklist.push_back(CalleeN);
388 LazyCallGraph::SCC *LazyCallGraph::formSCC(Node *RootN,
389 SmallVectorImpl<Node *> &NodeStack) {
390 // The tail of the stack is the new SCC. Allocate the SCC and pop the stack
392 SCC *NewSCC = new (SCCBPA.Allocate()) SCC();
394 SCCMap[RootN] = NewSCC;
395 NewSCC->Nodes.push_back(RootN);
397 while (!NodeStack.empty() && NodeStack.back()->DFSNumber > RootN->DFSNumber) {
398 Node *SCCN = NodeStack.pop_back_val();
399 assert(SCCN->LowLink >= RootN->LowLink &&
400 "We cannot have a low link in an SCC lower than its root on the "
402 SCCN->DFSNumber = SCCN->LowLink = -1;
404 SCCMap[SCCN] = NewSCC;
405 NewSCC->Nodes.push_back(SCCN);
407 RootN->DFSNumber = RootN->LowLink = -1;
409 // A final pass over all edges in the SCC (this remains linear as we only
410 // do this once when we build the SCC) to connect it to the parent sets of
412 bool IsLeafSCC = true;
413 for (Node *SCCN : NewSCC->Nodes)
414 for (Node &SCCChildN : *SCCN) {
415 if (SCCMap.lookup(&SCCChildN) == NewSCC)
417 SCC &ChildSCC = *SCCMap.lookup(&SCCChildN);
418 ChildSCC.ParentSCCs.insert(NewSCC);
422 // For the SCCs where we fine no child SCCs, add them to the leaf list.
424 LeafSCCs.push_back(NewSCC);
429 LazyCallGraph::SCC *LazyCallGraph::getNextSCCInPostOrder() {
430 // When the stack is empty, there are no more SCCs to walk in this graph.
431 if (DFSStack.empty()) {
432 // If we've handled all candidate entry nodes to the SCC forest, we're done.
433 if (SCCEntryNodes.empty())
436 Node &N = get(*SCCEntryNodes.pop_back_val());
437 N.LowLink = N.DFSNumber = 1;
439 DFSStack.push_back(std::make_pair(&N, N.begin()));
443 Node *N = DFSStack.back().first;
444 assert(N->DFSNumber != 0 && "We should always assign a DFS number "
445 "before placing a node onto the stack.");
447 bool Recurse = false; // Used to simulate recursing onto a child.
448 for (auto I = DFSStack.back().second, E = N->end(); I != E; ++I) {
450 if (ChildN.DFSNumber == 0) {
451 // Mark that we should start at this child when next this node is the
452 // top of the stack. We don't start at the next child to ensure this
453 // child's lowlink is reflected.
454 DFSStack.back().second = I;
456 // Recurse onto this node via a tail call.
457 assert(!SCCMap.count(&ChildN) &&
458 "Found a node with 0 DFS number but already in an SCC!");
459 ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
460 SCCEntryNodes.remove(&ChildN.getFunction());
461 DFSStack.push_back(std::make_pair(&ChildN, ChildN.begin()));
466 // Track the lowest link of the childen, if any are still in the stack.
467 assert(ChildN.LowLink != 0 &&
468 "Low-link must not be zero with a non-zero DFS number.");
469 if (ChildN.LowLink >= 0 && ChildN.LowLink < N->LowLink)
470 N->LowLink = ChildN.LowLink;
473 // Continue the outer loop when we exit the inner loop in order to
474 // recurse onto a child.
477 // No more children to process here, pop the node off the stack.
480 if (N->LowLink == N->DFSNumber)
481 // Form the new SCC out of the top of the DFS stack.
482 return formSCC(N, PendingSCCStack);
484 assert(!DFSStack.empty() && "We never found a viable root!");
486 // At this point we know that N cannot ever be an SCC root. Its low-link
487 // is not its dfs-number, and we've processed all of its children. It is
488 // just sitting here waiting until some node further down the stack gets
489 // low-link == dfs-number and pops it off as well. Move it to the pending
490 // stack which is pulled into the next SCC to be formed.
491 PendingSCCStack.push_back(N);
495 char LazyCallGraphAnalysis::PassID;
497 LazyCallGraphPrinterPass::LazyCallGraphPrinterPass(raw_ostream &OS) : OS(OS) {}
499 static void printNodes(raw_ostream &OS, LazyCallGraph::Node &N,
500 SmallPtrSetImpl<LazyCallGraph::Node *> &Printed) {
501 // Recurse depth first through the nodes.
502 for (LazyCallGraph::Node &ChildN : N)
503 if (Printed.insert(&ChildN))
504 printNodes(OS, ChildN, Printed);
506 OS << " Call edges in function: " << N.getFunction().getName() << "\n";
507 for (LazyCallGraph::iterator I = N.begin(), E = N.end(); I != E; ++I)
508 OS << " -> " << I->getFunction().getName() << "\n";
513 static void printSCC(raw_ostream &OS, LazyCallGraph::SCC &SCC) {
514 ptrdiff_t SCCSize = std::distance(SCC.begin(), SCC.end());
515 OS << " SCC with " << SCCSize << " functions:\n";
517 for (LazyCallGraph::Node *N : SCC)
518 OS << " " << N->getFunction().getName() << "\n";
523 PreservedAnalyses LazyCallGraphPrinterPass::run(Module *M,
524 ModuleAnalysisManager *AM) {
525 LazyCallGraph &G = AM->getResult<LazyCallGraphAnalysis>(M);
527 OS << "Printing the call graph for module: " << M->getModuleIdentifier()
530 SmallPtrSet<LazyCallGraph::Node *, 16> Printed;
531 for (LazyCallGraph::Node &N : G)
532 if (Printed.insert(&N))
533 printNodes(OS, N, Printed);
535 for (LazyCallGraph::SCC &SCC : G.postorder_sccs())
538 return PreservedAnalyses::all();