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 // Direct recursion doesn't impact the SCC graph at all.
192 if (&Caller == &Callee)
195 // We're going to do a full mini-Tarjan's walk using a local stack here.
197 SmallVector<std::pair<Node *, Node::iterator>, 4> DFSStack;
198 SmallVector<Node *, 4> PendingSCCStack;
200 // The worklist is every node in the original SCC.
201 SmallVector<Node *, 1> Worklist;
202 Worklist.swap(Nodes);
203 for (Node *N : Worklist) {
204 // The nodes formerly in this SCC are no longer in any SCC.
209 assert(Worklist.size() > 1 && "We have to have at least two nodes to have an "
210 "edge between them that is within the SCC.");
212 // The callee can already reach every node in this SCC (by definition). It is
213 // the only node we know will stay inside this SCC. Everything which
214 // transitively reaches Callee will also remain in the SCC. To model this we
215 // incrementally add any chain of nodes which reaches something in the new
216 // node set to the new node set. This short circuits one side of the Tarjan's
221 if (DFSStack.empty()) {
222 // Clear off any nodes which have already been visited in the DFS.
223 while (!Worklist.empty() && Worklist.back()->DFSNumber != 0)
225 if (Worklist.empty())
227 Node *N = Worklist.pop_back_val();
228 N->LowLink = N->DFSNumber = 1;
230 DFSStack.push_back(std::make_pair(N, N->begin()));
231 assert(PendingSCCStack.empty() && "Cannot start a fresh DFS walk with "
232 "pending nodes from a prior walk.");
235 Node *N = DFSStack.back().first;
236 assert(N->DFSNumber != 0 && "We should always assign a DFS number "
237 "before placing a node onto the stack.");
239 // We simulate recursion by popping out of the nested loop and continuing.
240 bool Recurse = false;
241 for (auto I = DFSStack.back().second, E = N->end(); I != E; ++I) {
243 if (SCC *ChildSCC = G.SCCMap.lookup(&ChildN)) {
244 // Check if we have reached a node in the new (known connected) set of
245 // this SCC. If so, the entire stack is necessarily in that set and we
247 if (ChildSCC == this) {
248 while (!PendingSCCStack.empty())
249 insert(G, *PendingSCCStack.pop_back_val());
250 while (!DFSStack.empty())
251 insert(G, *DFSStack.pop_back_val().first);
256 // If this child isn't currently in this SCC, no need to process it.
257 // However, we do need to remove this SCC from its SCC's parent set.
258 ChildSCC->ParentSCCs.erase(this);
262 if (ChildN.DFSNumber == 0) {
263 // Mark that we should start at this child when next this node is the
264 // top of the stack. We don't start at the next child to ensure this
265 // child's lowlink is reflected.
266 DFSStack.back().second = I;
268 // Recurse onto this node via a tail call.
269 ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
270 DFSStack.push_back(std::make_pair(&ChildN, ChildN.begin()));
275 // Track the lowest link of the childen, if any are still in the stack.
276 // Any child not on the stack will have a LowLink of -1.
277 assert(ChildN.LowLink != 0 &&
278 "Low-link must not be zero with a non-zero DFS number.");
279 if (ChildN.LowLink >= 0 && ChildN.LowLink < N->LowLink)
280 N->LowLink = ChildN.LowLink;
285 // No more children to process, pop it off the core DFS stack.
288 if (N->LowLink == N->DFSNumber) {
289 ResultSCCs.push_back(G.formSCC(N, PendingSCCStack));
293 assert(!DFSStack.empty() && "We shouldn't have an empty stack!");
295 // At this point we know that N cannot ever be an SCC root. Its low-link
296 // is not its dfs-number, and we've processed all of its children. It is
297 // just sitting here waiting until some node further down the stack gets
298 // low-link == dfs-number and pops it off as well. Move it to the pending
299 // stack which is pulled into the next SCC to be formed.
300 PendingSCCStack.push_back(N);
303 // Now we need to reconnect the current SCC to the graph.
304 bool IsLeafSCC = true;
305 for (Node *N : Nodes) {
306 for (Node &ChildN : *N) {
307 SCC &ChildSCC = *G.SCCMap.lookup(&ChildN);
308 if (&ChildSCC == this)
310 ChildSCC.ParentSCCs.insert(this);
315 if (ResultSCCs.size() > 1)
316 assert(!IsLeafSCC && "This SCC cannot be a leaf as we have split out new "
317 "SCCs by removing this edge.");
318 if (!std::any_of(G.LeafSCCs.begin(), G.LeafSCCs.end(),
319 [&](SCC *C) { return C == this; }))
320 assert(!IsLeafSCC && "This SCC cannot be a leaf as it already had child "
321 "SCCs before we removed this edge.");
323 // If this SCC stopped being a leaf through this edge removal, remove it from
324 // the leaf SCC list.
325 if (!IsLeafSCC && ResultSCCs.size() > 1)
326 G.LeafSCCs.erase(std::remove(G.LeafSCCs.begin(), G.LeafSCCs.end(), this),
329 // Return the new list of SCCs.
333 void LazyCallGraph::removeEdge(Node &CallerN, Function &Callee) {
334 auto IndexMapI = CallerN.CalleeIndexMap.find(&Callee);
335 assert(IndexMapI != CallerN.CalleeIndexMap.end() &&
336 "Callee not in the callee set for the caller?");
338 Node *CalleeN = CallerN.Callees[IndexMapI->second].dyn_cast<Node *>();
339 CallerN.Callees.erase(CallerN.Callees.begin() + IndexMapI->second);
340 CallerN.CalleeIndexMap.erase(IndexMapI);
342 SCC *CallerC = SCCMap.lookup(&CallerN);
344 // We can only remove edges when the edge isn't actively participating in
345 // a DFS walk. Either it must have been popped into an SCC, or it must not
346 // yet have been reached by the DFS walk. Assert the latter here.
347 assert(std::all_of(DFSStack.begin(), DFSStack.end(),
348 [&](const std::pair<Node *, iterator> &StackEntry) {
349 return StackEntry.first != &CallerN;
351 "Found the caller on the DFSStack!");
355 assert(CalleeN && "If the caller is in an SCC, we have to have explored all "
356 "its transitively called functions.");
358 SCC *CalleeC = SCCMap.lookup(CalleeN);
360 "The caller has an SCC, and thus by necessity so does the callee.");
362 // The easy case is when they are different SCCs.
363 if (CallerC != CalleeC) {
364 CallerC->removeEdge(*this, CallerN.getFunction(), Callee, *CalleeC);
368 // The hard case is when we remove an edge within a SCC. This may cause new
369 // SCCs to need to be added to the graph.
370 CallerC->removeInternalEdge(*this, CallerN, *CalleeN);
373 LazyCallGraph::Node &LazyCallGraph::insertInto(Function &F, Node *&MappedN) {
374 return *new (MappedN = BPA.Allocate()) Node(*this, F);
377 void LazyCallGraph::updateGraphPtrs() {
378 // Process all nodes updating the graph pointers.
379 SmallVector<Node *, 16> Worklist;
380 for (auto &Entry : EntryNodes)
381 if (Node *EntryN = Entry.dyn_cast<Node *>())
382 Worklist.push_back(EntryN);
384 while (!Worklist.empty()) {
385 Node *N = Worklist.pop_back_val();
387 for (auto &Callee : N->Callees)
388 if (Node *CalleeN = Callee.dyn_cast<Node *>())
389 Worklist.push_back(CalleeN);
393 LazyCallGraph::SCC *LazyCallGraph::formSCC(Node *RootN,
394 SmallVectorImpl<Node *> &NodeStack) {
395 // The tail of the stack is the new SCC. Allocate the SCC and pop the stack
397 SCC *NewSCC = new (SCCBPA.Allocate()) SCC();
399 while (!NodeStack.empty() && NodeStack.back()->DFSNumber > RootN->DFSNumber) {
400 assert(NodeStack.back()->LowLink >= RootN->LowLink &&
401 "We cannot have a low link in an SCC lower than its root on the "
403 NewSCC->insert(*this, *NodeStack.pop_back_val());
405 NewSCC->insert(*this, *RootN);
407 // A final pass over all edges in the SCC (this remains linear as we only
408 // do this once when we build the SCC) to connect it to the parent sets of
410 bool IsLeafSCC = true;
411 for (Node *SCCN : NewSCC->Nodes)
412 for (Node &SCCChildN : *SCCN) {
413 if (SCCMap.lookup(&SCCChildN) == NewSCC)
415 SCC &ChildSCC = *SCCMap.lookup(&SCCChildN);
416 ChildSCC.ParentSCCs.insert(NewSCC);
420 // For the SCCs where we fine no child SCCs, add them to the leaf list.
422 LeafSCCs.push_back(NewSCC);
427 LazyCallGraph::SCC *LazyCallGraph::getNextSCCInPostOrder() {
428 // When the stack is empty, there are no more SCCs to walk in this graph.
429 if (DFSStack.empty()) {
430 // If we've handled all candidate entry nodes to the SCC forest, we're done.
431 if (SCCEntryNodes.empty())
434 Node &N = get(*SCCEntryNodes.pop_back_val());
435 N.LowLink = N.DFSNumber = 1;
437 DFSStack.push_back(std::make_pair(&N, N.begin()));
441 Node *N = DFSStack.back().first;
442 assert(N->DFSNumber != 0 && "We should always assign a DFS number "
443 "before placing a node onto the stack.");
445 bool Recurse = false; // Used to simulate recursing onto a child.
446 for (auto I = DFSStack.back().second, E = N->end(); I != E; ++I) {
448 if (ChildN.DFSNumber == 0) {
449 // Mark that we should start at this child when next this node is the
450 // top of the stack. We don't start at the next child to ensure this
451 // child's lowlink is reflected.
452 DFSStack.back().second = I;
454 // Recurse onto this node via a tail call.
455 assert(!SCCMap.count(&ChildN) &&
456 "Found a node with 0 DFS number but already in an SCC!");
457 ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
458 SCCEntryNodes.remove(&ChildN.getFunction());
459 DFSStack.push_back(std::make_pair(&ChildN, ChildN.begin()));
464 // Track the lowest link of the childen, if any are still in the stack.
465 assert(ChildN.LowLink != 0 &&
466 "Low-link must not be zero with a non-zero DFS number.");
467 if (ChildN.LowLink >= 0 && ChildN.LowLink < N->LowLink)
468 N->LowLink = ChildN.LowLink;
471 // Continue the outer loop when we exit the inner loop in order to
472 // recurse onto a child.
475 // No more children to process here, pop the node off the stack.
478 if (N->LowLink == N->DFSNumber)
479 // Form the new SCC out of the top of the DFS stack.
480 return formSCC(N, PendingSCCStack);
482 assert(!DFSStack.empty() && "We never found a viable root!");
484 // At this point we know that N cannot ever be an SCC root. Its low-link
485 // is not its dfs-number, and we've processed all of its children. It is
486 // just sitting here waiting until some node further down the stack gets
487 // low-link == dfs-number and pops it off as well. Move it to the pending
488 // stack which is pulled into the next SCC to be formed.
489 PendingSCCStack.push_back(N);
493 char LazyCallGraphAnalysis::PassID;
495 LazyCallGraphPrinterPass::LazyCallGraphPrinterPass(raw_ostream &OS) : OS(OS) {}
497 static void printNodes(raw_ostream &OS, LazyCallGraph::Node &N,
498 SmallPtrSetImpl<LazyCallGraph::Node *> &Printed) {
499 // Recurse depth first through the nodes.
500 for (LazyCallGraph::Node &ChildN : N)
501 if (Printed.insert(&ChildN))
502 printNodes(OS, ChildN, Printed);
504 OS << " Call edges in function: " << N.getFunction().getName() << "\n";
505 for (LazyCallGraph::iterator I = N.begin(), E = N.end(); I != E; ++I)
506 OS << " -> " << I->getFunction().getName() << "\n";
511 static void printSCC(raw_ostream &OS, LazyCallGraph::SCC &SCC) {
512 ptrdiff_t SCCSize = std::distance(SCC.begin(), SCC.end());
513 OS << " SCC with " << SCCSize << " functions:\n";
515 for (LazyCallGraph::Node *N : SCC)
516 OS << " " << N->getFunction().getName() << "\n";
521 PreservedAnalyses LazyCallGraphPrinterPass::run(Module *M,
522 ModuleAnalysisManager *AM) {
523 LazyCallGraph &G = AM->getResult<LazyCallGraphAnalysis>(M);
525 OS << "Printing the call graph for module: " << M->getModuleIdentifier()
528 SmallPtrSet<LazyCallGraph::Node *, 16> Printed;
529 for (LazyCallGraph::Node &N : G)
530 if (Printed.insert(&N))
531 printNodes(OS, N, Printed);
533 for (LazyCallGraph::SCC &SCC : G.postorder_sccs())
536 return PreservedAnalyses::all();