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::insert(LazyCallGraph &G, Node &N) {
135 N.DFSNumber = N.LowLink = -1;
140 void LazyCallGraph::SCC::removeEdge(LazyCallGraph &G, Function &Caller,
141 Function &Callee, SCC &CalleeC) {
142 assert(std::find(G.LeafSCCs.begin(), G.LeafSCCs.end(), this) ==
144 "Cannot have a leaf SCC caller with a different SCC callee.");
146 bool HasOtherCallToCalleeC = false;
147 bool HasOtherCallOutsideSCC = false;
148 for (Node *N : *this) {
149 for (Node &Callee : *N) {
150 SCC &OtherCalleeC = *G.SCCMap.lookup(&Callee);
151 if (&OtherCalleeC == &CalleeC) {
152 HasOtherCallToCalleeC = true;
155 if (&OtherCalleeC != this)
156 HasOtherCallOutsideSCC = true;
158 if (HasOtherCallToCalleeC)
161 // Because the SCCs form a DAG, deleting such an edge cannot change the set
162 // of SCCs in the graph. However, it may cut an edge of the SCC DAG, making
163 // the caller no longer a parent of the callee. Walk the other call edges
164 // in the caller to tell.
165 if (!HasOtherCallToCalleeC) {
166 bool Removed = CalleeC.ParentSCCs.erase(this);
169 "Did not find the caller SCC in the callee SCC's parent list!");
171 // It may orphan an SCC if it is the last edge reaching it, but that does
172 // not violate any invariants of the graph.
173 if (CalleeC.ParentSCCs.empty())
174 DEBUG(dbgs() << "LCG: Update removing " << Caller.getName() << " -> "
175 << Callee.getName() << " edge orphaned the callee's SCC!\n");
178 // It may make the Caller SCC a leaf SCC.
179 if (!HasOtherCallOutsideSCC)
180 G.LeafSCCs.push_back(this);
183 SmallVector<LazyCallGraph::SCC *, 1>
184 LazyCallGraph::SCC::removeInternalEdge(LazyCallGraph &G, Node &Caller,
186 // We return a list of the resulting SCCs, where 'this' is always the first
188 SmallVector<SCC *, 1> ResultSCCs;
189 ResultSCCs.push_back(this);
191 // We're going to do a full mini-Tarjan's walk using a local stack here.
193 SmallVector<std::pair<Node *, Node::iterator>, 4> DFSStack;
194 SmallVector<Node *, 4> PendingSCCStack;
196 // The worklist is every node in the original SCC.
197 SmallVector<Node *, 1> Worklist;
198 Worklist.swap(Nodes);
199 for (Node *N : Worklist) {
200 // The nodes formerly in this SCC are no longer in any SCC.
206 // The callee can already reach every node in this SCC (by definition). It is
207 // the only node we know will stay inside this SCC. Everything which
208 // transitively reaches Callee will also remain in the SCC. To model this we
209 // incrementally add any chain of nodes which reaches something in the new
210 // node set to the new node set. This short circuits one side of the Tarjan's
215 if (DFSStack.empty()) {
216 // Clear off any nodes which have already been visited in the DFS.
217 while (!Worklist.empty() && Worklist.back()->DFSNumber != 0)
219 if (Worklist.empty())
221 Node *N = Worklist.pop_back_val();
222 N->LowLink = N->DFSNumber = 1;
224 DFSStack.push_back(std::make_pair(N, N->begin()));
225 assert(PendingSCCStack.empty() && "Cannot start a fresh DFS walk with "
226 "pending nodes from a prior walk.");
229 Node *N = DFSStack.back().first;
230 assert(N->DFSNumber != 0 && "We should always assign a DFS number "
231 "before placing a node onto the stack.");
233 // We simulate recursion by popping out of the nested loop and continuing.
234 bool Recurse = false;
235 for (auto I = DFSStack.back().second, E = N->end(); I != E; ++I) {
237 if (SCC *ChildSCC = G.SCCMap.lookup(&ChildN)) {
238 // Check if we have reached a node in the new (known connected) set of
239 // this SCC. If so, the entire stack is necessarily in that set and we
241 if (ChildSCC == this) {
242 while (!PendingSCCStack.empty())
243 insert(G, *PendingSCCStack.pop_back_val());
244 while (!DFSStack.empty())
245 insert(G, *DFSStack.pop_back_val().first);
250 // If this child isn't currently in this SCC, no need to process it.
251 // However, we do need to remove this SCC from its SCC's parent set.
252 ChildSCC->ParentSCCs.erase(this);
256 if (ChildN.DFSNumber == 0) {
257 // Mark that we should start at this child when next this node is the
258 // top of the stack. We don't start at the next child to ensure this
259 // child's lowlink is reflected.
260 DFSStack.back().second = I;
262 // Recurse onto this node via a tail call.
263 ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
264 DFSStack.push_back(std::make_pair(&ChildN, ChildN.begin()));
269 // Track the lowest link of the childen, if any are still in the stack.
270 // Any child not on the stack will have a LowLink of -1.
271 assert(ChildN.LowLink != 0 &&
272 "Low-link must not be zero with a non-zero DFS number.");
273 if (ChildN.LowLink >= 0 && ChildN.LowLink < N->LowLink)
274 N->LowLink = ChildN.LowLink;
279 // No more children to process, pop it off the core DFS stack.
282 if (N->LowLink == N->DFSNumber) {
283 ResultSCCs.push_back(G.formSCC(N, PendingSCCStack));
287 assert(!DFSStack.empty() && "We shouldn't have an empty stack!");
289 // At this point we know that N cannot ever be an SCC root. Its low-link
290 // is not its dfs-number, and we've processed all of its children. It is
291 // just sitting here waiting until some node further down the stack gets
292 // low-link == dfs-number and pops it off as well. Move it to the pending
293 // stack which is pulled into the next SCC to be formed.
294 PendingSCCStack.push_back(N);
297 // Now we need to reconnect the current SCC to the graph.
298 bool IsLeafSCC = true;
299 for (Node *N : Nodes) {
300 for (Node &ChildN : *N) {
301 SCC &ChildSCC = *G.SCCMap.lookup(&ChildN);
302 if (&ChildSCC == this)
304 ChildSCC.ParentSCCs.insert(this);
309 if (ResultSCCs.size() > 1)
310 assert(!IsLeafSCC && "This SCC cannot be a leaf as we have split out new "
311 "SCCs by removing this edge.");
312 if (!std::any_of(G.LeafSCCs.begin(), G.LeafSCCs.end(),
313 [&](SCC *C) { return C == this; }))
314 assert(!IsLeafSCC && "This SCC cannot be a leaf as it already had child "
315 "SCCs before we removed this edge.");
317 // If this SCC stopped being a leaf through this edge removal, remove it from
318 // the leaf SCC list.
319 if (!IsLeafSCC && ResultSCCs.size() > 1)
320 G.LeafSCCs.erase(std::remove(G.LeafSCCs.begin(), G.LeafSCCs.end(), this),
323 // Return the new list of SCCs.
327 void LazyCallGraph::removeEdge(Node &CallerN, Function &Callee) {
328 auto IndexMapI = CallerN.CalleeIndexMap.find(&Callee);
329 assert(IndexMapI != CallerN.CalleeIndexMap.end() &&
330 "Callee not in the callee set for the caller?");
332 Node *CalleeN = CallerN.Callees[IndexMapI->second].dyn_cast<Node *>();
333 CallerN.Callees.erase(CallerN.Callees.begin() + IndexMapI->second);
334 CallerN.CalleeIndexMap.erase(IndexMapI);
336 SCC *CallerC = SCCMap.lookup(&CallerN);
338 // We can only remove edges when the edge isn't actively participating in
339 // a DFS walk. Either it must have been popped into an SCC, or it must not
340 // yet have been reached by the DFS walk. Assert the latter here.
341 assert(std::all_of(DFSStack.begin(), DFSStack.end(),
342 [&](const std::pair<Node *, iterator> &StackEntry) {
343 return StackEntry.first != &CallerN;
345 "Found the caller on the DFSStack!");
349 assert(CalleeN && "If the caller is in an SCC, we have to have explored all "
350 "its transitively called functions.");
352 SCC *CalleeC = SCCMap.lookup(CalleeN);
354 "The caller has an SCC, and thus by necessity so does the callee.");
356 // The easy case is when they are different SCCs.
357 if (CallerC != CalleeC) {
358 CallerC->removeEdge(*this, CallerN.getFunction(), Callee, *CalleeC);
362 // The hard case is when we remove an edge within a SCC. This may cause new
363 // SCCs to need to be added to the graph.
364 CallerC->removeInternalEdge(*this, CallerN, *CalleeN);
367 LazyCallGraph::Node &LazyCallGraph::insertInto(Function &F, Node *&MappedN) {
368 return *new (MappedN = BPA.Allocate()) Node(*this, F);
371 void LazyCallGraph::updateGraphPtrs() {
372 // Process all nodes updating the graph pointers.
373 SmallVector<Node *, 16> Worklist;
374 for (auto &Entry : EntryNodes)
375 if (Node *EntryN = Entry.dyn_cast<Node *>())
376 Worklist.push_back(EntryN);
378 while (!Worklist.empty()) {
379 Node *N = Worklist.pop_back_val();
381 for (auto &Callee : N->Callees)
382 if (Node *CalleeN = Callee.dyn_cast<Node *>())
383 Worklist.push_back(CalleeN);
387 LazyCallGraph::SCC *LazyCallGraph::formSCC(Node *RootN,
388 SmallVectorImpl<Node *> &NodeStack) {
389 // The tail of the stack is the new SCC. Allocate the SCC and pop the stack
391 SCC *NewSCC = new (SCCBPA.Allocate()) SCC();
393 while (!NodeStack.empty() && NodeStack.back()->DFSNumber > RootN->DFSNumber) {
394 assert(NodeStack.back()->LowLink >= RootN->LowLink &&
395 "We cannot have a low link in an SCC lower than its root on the "
397 NewSCC->insert(*this, *NodeStack.pop_back_val());
399 NewSCC->insert(*this, *RootN);
401 // A final pass over all edges in the SCC (this remains linear as we only
402 // do this once when we build the SCC) to connect it to the parent sets of
404 bool IsLeafSCC = true;
405 for (Node *SCCN : NewSCC->Nodes)
406 for (Node &SCCChildN : *SCCN) {
407 if (SCCMap.lookup(&SCCChildN) == NewSCC)
409 SCC &ChildSCC = *SCCMap.lookup(&SCCChildN);
410 ChildSCC.ParentSCCs.insert(NewSCC);
414 // For the SCCs where we fine no child SCCs, add them to the leaf list.
416 LeafSCCs.push_back(NewSCC);
421 LazyCallGraph::SCC *LazyCallGraph::getNextSCCInPostOrder() {
422 // When the stack is empty, there are no more SCCs to walk in this graph.
423 if (DFSStack.empty()) {
424 // If we've handled all candidate entry nodes to the SCC forest, we're done.
425 if (SCCEntryNodes.empty())
428 Node &N = get(*SCCEntryNodes.pop_back_val());
429 N.LowLink = N.DFSNumber = 1;
431 DFSStack.push_back(std::make_pair(&N, N.begin()));
435 Node *N = DFSStack.back().first;
436 assert(N->DFSNumber != 0 && "We should always assign a DFS number "
437 "before placing a node onto the stack.");
439 bool Recurse = false; // Used to simulate recursing onto a child.
440 for (auto I = DFSStack.back().second, E = N->end(); I != E; ++I) {
442 if (ChildN.DFSNumber == 0) {
443 // Mark that we should start at this child when next this node is the
444 // top of the stack. We don't start at the next child to ensure this
445 // child's lowlink is reflected.
446 DFSStack.back().second = I;
448 // Recurse onto this node via a tail call.
449 assert(!SCCMap.count(&ChildN) &&
450 "Found a node with 0 DFS number but already in an SCC!");
451 ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
452 SCCEntryNodes.remove(&ChildN.getFunction());
453 DFSStack.push_back(std::make_pair(&ChildN, ChildN.begin()));
458 // Track the lowest link of the childen, if any are still in the stack.
459 assert(ChildN.LowLink != 0 &&
460 "Low-link must not be zero with a non-zero DFS number.");
461 if (ChildN.LowLink >= 0 && ChildN.LowLink < N->LowLink)
462 N->LowLink = ChildN.LowLink;
465 // Continue the outer loop when we exit the inner loop in order to
466 // recurse onto a child.
469 // No more children to process here, pop the node off the stack.
472 if (N->LowLink == N->DFSNumber)
473 // Form the new SCC out of the top of the DFS stack.
474 return formSCC(N, PendingSCCStack);
476 assert(!DFSStack.empty() && "We never found a viable root!");
478 // At this point we know that N cannot ever be an SCC root. Its low-link
479 // is not its dfs-number, and we've processed all of its children. It is
480 // just sitting here waiting until some node further down the stack gets
481 // low-link == dfs-number and pops it off as well. Move it to the pending
482 // stack which is pulled into the next SCC to be formed.
483 PendingSCCStack.push_back(N);
487 char LazyCallGraphAnalysis::PassID;
489 LazyCallGraphPrinterPass::LazyCallGraphPrinterPass(raw_ostream &OS) : OS(OS) {}
491 static void printNodes(raw_ostream &OS, LazyCallGraph::Node &N,
492 SmallPtrSetImpl<LazyCallGraph::Node *> &Printed) {
493 // Recurse depth first through the nodes.
494 for (LazyCallGraph::Node &ChildN : N)
495 if (Printed.insert(&ChildN))
496 printNodes(OS, ChildN, Printed);
498 OS << " Call edges in function: " << N.getFunction().getName() << "\n";
499 for (LazyCallGraph::iterator I = N.begin(), E = N.end(); I != E; ++I)
500 OS << " -> " << I->getFunction().getName() << "\n";
505 static void printSCC(raw_ostream &OS, LazyCallGraph::SCC &SCC) {
506 ptrdiff_t SCCSize = std::distance(SCC.begin(), SCC.end());
507 OS << " SCC with " << SCCSize << " functions:\n";
509 for (LazyCallGraph::Node *N : SCC)
510 OS << " " << N->getFunction().getName() << "\n";
515 PreservedAnalyses LazyCallGraphPrinterPass::run(Module *M,
516 ModuleAnalysisManager *AM) {
517 LazyCallGraph &G = AM->getResult<LazyCallGraphAnalysis>(M);
519 OS << "Printing the call graph for module: " << M->getModuleIdentifier()
522 SmallPtrSet<LazyCallGraph::Node *, 16> Printed;
523 for (LazyCallGraph::Node &N : G)
524 if (Printed.insert(&N))
525 printNodes(OS, N, Printed);
527 for (LazyCallGraph::SCC &SCC : G.postorder_sccs())
530 return PreservedAnalyses::all();