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::removeInterSCCEdge(Node &CallerN, Node &CalleeN) {
191 // First remove it from the node.
192 CallerN.removeEdgeInternal(CalleeN.getFunction());
194 assert(G->SCCMap.lookup(&CallerN) == this &&
195 "The caller must be a member of this SCC.");
197 SCC &CalleeC = *G->SCCMap.lookup(&CalleeN);
198 assert(&CalleeC != this &&
199 "This API only supports the rmoval of inter-SCC edges.");
201 assert(std::find(G->LeafSCCs.begin(), G->LeafSCCs.end(), this) ==
203 "Cannot have a leaf SCC caller with a different SCC callee.");
205 bool HasOtherCallToCalleeC = false;
206 bool HasOtherCallOutsideSCC = false;
207 for (Node *N : *this) {
208 for (Node &OtherCalleeN : *N) {
209 SCC &OtherCalleeC = *G->SCCMap.lookup(&OtherCalleeN);
210 if (&OtherCalleeC == &CalleeC) {
211 HasOtherCallToCalleeC = true;
214 if (&OtherCalleeC != this)
215 HasOtherCallOutsideSCC = true;
217 if (HasOtherCallToCalleeC)
220 // Because the SCCs form a DAG, deleting such an edge cannot change the set
221 // of SCCs in the graph. However, it may cut an edge of the SCC DAG, making
222 // the caller no longer a parent of the callee. Walk the other call edges
223 // in the caller to tell.
224 if (!HasOtherCallToCalleeC) {
225 bool Removed = CalleeC.ParentSCCs.erase(this);
228 "Did not find the caller SCC in the callee SCC's parent list!");
230 // It may orphan an SCC if it is the last edge reaching it, but that does
231 // not violate any invariants of the graph.
232 if (CalleeC.ParentSCCs.empty())
233 DEBUG(dbgs() << "LCG: Update removing " << CallerN.getFunction().getName()
234 << " -> " << CalleeN.getFunction().getName()
235 << " edge orphaned the callee's SCC!\n");
238 // It may make the Caller SCC a leaf SCC.
239 if (!HasOtherCallOutsideSCC)
240 G->LeafSCCs.push_back(this);
243 void LazyCallGraph::SCC::internalDFS(
244 SmallVectorImpl<std::pair<Node *, Node::iterator>> &DFSStack,
245 SmallVectorImpl<Node *> &PendingSCCStack, Node *N,
246 SmallVectorImpl<SCC *> &ResultSCCs) {
247 Node::iterator I = N->begin();
248 N->LowLink = N->DFSNumber = 1;
249 int NextDFSNumber = 2;
251 assert(N->DFSNumber != 0 && "We should always assign a DFS number "
252 "before processing a node.");
254 // We simulate recursion by popping out of the nested loop and continuing.
255 Node::iterator E = N->end();
258 if (SCC *ChildSCC = G->SCCMap.lookup(&ChildN)) {
259 // Check if we have reached a node in the new (known connected) set of
260 // this SCC. If so, the entire stack is necessarily in that set and we
262 if (ChildSCC == this) {
264 while (!PendingSCCStack.empty())
265 insert(*PendingSCCStack.pop_back_val());
266 while (!DFSStack.empty())
267 insert(*DFSStack.pop_back_val().first);
271 // If this child isn't currently in this SCC, no need to process it.
272 // However, we do need to remove this SCC from its SCC's parent set.
273 ChildSCC->ParentSCCs.erase(this);
278 if (ChildN.DFSNumber == 0) {
279 // Mark that we should start at this child when next this node is the
280 // top of the stack. We don't start at the next child to ensure this
281 // child's lowlink is reflected.
282 DFSStack.push_back(std::make_pair(N, I));
284 // Continue, resetting to the child node.
285 ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
292 // Track the lowest link of the childen, if any are still in the stack.
293 // Any child not on the stack will have a LowLink of -1.
294 assert(ChildN.LowLink != 0 &&
295 "Low-link must not be zero with a non-zero DFS number.");
296 if (ChildN.LowLink >= 0 && ChildN.LowLink < N->LowLink)
297 N->LowLink = ChildN.LowLink;
301 if (N->LowLink == N->DFSNumber) {
302 ResultSCCs.push_back(G->formSCC(N, PendingSCCStack));
303 if (DFSStack.empty())
306 // At this point we know that N cannot ever be an SCC root. Its low-link
307 // is not its dfs-number, and we've processed all of its children. It is
308 // just sitting here waiting until some node further down the stack gets
309 // low-link == dfs-number and pops it off as well. Move it to the pending
310 // stack which is pulled into the next SCC to be formed.
311 PendingSCCStack.push_back(N);
313 assert(!DFSStack.empty() && "We shouldn't have an empty stack!");
316 N = DFSStack.back().first;
317 I = DFSStack.back().second;
322 SmallVector<LazyCallGraph::SCC *, 1>
323 LazyCallGraph::SCC::removeIntraSCCEdge(Node &CallerN,
325 // First remove it from the node.
326 CallerN.removeEdgeInternal(CalleeN.getFunction());
328 // We return a list of the resulting *new* SCCs in postorder.
329 SmallVector<SCC *, 1> ResultSCCs;
331 // Direct recursion doesn't impact the SCC graph at all.
332 if (&CallerN == &CalleeN)
335 // The worklist is every node in the original SCC.
336 SmallVector<Node *, 1> Worklist;
337 Worklist.swap(Nodes);
338 for (Node *N : Worklist) {
339 // The nodes formerly in this SCC are no longer in any SCC.
344 assert(Worklist.size() > 1 && "We have to have at least two nodes to have an "
345 "edge between them that is within the SCC.");
347 // The callee can already reach every node in this SCC (by definition). It is
348 // the only node we know will stay inside this SCC. Everything which
349 // transitively reaches Callee will also remain in the SCC. To model this we
350 // incrementally add any chain of nodes which reaches something in the new
351 // node set to the new node set. This short circuits one side of the Tarjan's
355 // We're going to do a full mini-Tarjan's walk using a local stack here.
356 SmallVector<std::pair<Node *, Node::iterator>, 4> DFSStack;
357 SmallVector<Node *, 4> PendingSCCStack;
359 Node *N = Worklist.pop_back_val();
360 if (N->DFSNumber == 0)
361 internalDFS(DFSStack, PendingSCCStack, N, ResultSCCs);
363 assert(DFSStack.empty() && "Didn't flush the entire DFS stack!");
364 assert(PendingSCCStack.empty() && "Didn't flush all pending SCC nodes!");
365 } while (!Worklist.empty());
367 // Now we need to reconnect the current SCC to the graph.
368 bool IsLeafSCC = true;
369 for (Node *N : Nodes) {
370 for (Node &ChildN : *N) {
371 SCC &ChildSCC = *G->SCCMap.lookup(&ChildN);
372 if (&ChildSCC == this)
374 ChildSCC.ParentSCCs.insert(this);
379 if (!ResultSCCs.empty())
380 assert(!IsLeafSCC && "This SCC cannot be a leaf as we have split out new "
381 "SCCs by removing this edge.");
382 if (!std::any_of(G->LeafSCCs.begin(), G->LeafSCCs.end(),
383 [&](SCC *C) { return C == this; }))
384 assert(!IsLeafSCC && "This SCC cannot be a leaf as it already had child "
385 "SCCs before we removed this edge.");
387 // If this SCC stopped being a leaf through this edge removal, remove it from
388 // the leaf SCC list.
389 if (!IsLeafSCC && !ResultSCCs.empty())
390 G->LeafSCCs.erase(std::remove(G->LeafSCCs.begin(), G->LeafSCCs.end(), this),
393 // Return the new list of SCCs.
397 void LazyCallGraph::insertEdge(Node &CallerN, Function &Callee) {
398 assert(SCCMap.empty() && DFSStack.empty() &&
399 "This method cannot be called after SCCs have been formed!");
401 return CallerN.insertEdgeInternal(Callee);
404 void LazyCallGraph::removeEdge(Node &CallerN, Function &Callee) {
405 assert(SCCMap.empty() && DFSStack.empty() &&
406 "This method cannot be called after SCCs have been formed!");
408 return CallerN.removeEdgeInternal(Callee);
411 LazyCallGraph::Node &LazyCallGraph::insertInto(Function &F, Node *&MappedN) {
412 return *new (MappedN = BPA.Allocate()) Node(*this, F);
415 void LazyCallGraph::updateGraphPtrs() {
416 // Process all nodes updating the graph pointers.
418 SmallVector<Node *, 16> Worklist;
419 for (auto &Entry : EntryNodes)
420 if (Node *EntryN = Entry.dyn_cast<Node *>())
421 Worklist.push_back(EntryN);
423 while (!Worklist.empty()) {
424 Node *N = Worklist.pop_back_val();
426 for (auto &Callee : N->Callees)
427 if (!Callee.isNull())
428 if (Node *CalleeN = Callee.dyn_cast<Node *>())
429 Worklist.push_back(CalleeN);
433 // Process all SCCs updating the graph pointers.
435 SmallVector<SCC *, 16> Worklist(LeafSCCs.begin(), LeafSCCs.end());
437 while (!Worklist.empty()) {
438 SCC *C = Worklist.pop_back_val();
440 Worklist.insert(Worklist.end(), C->ParentSCCs.begin(),
441 C->ParentSCCs.end());
446 LazyCallGraph::SCC *LazyCallGraph::formSCC(Node *RootN,
447 SmallVectorImpl<Node *> &NodeStack) {
448 // The tail of the stack is the new SCC. Allocate the SCC and pop the stack
450 SCC *NewSCC = new (SCCBPA.Allocate()) SCC(*this);
452 while (!NodeStack.empty() && NodeStack.back()->DFSNumber > RootN->DFSNumber) {
453 assert(NodeStack.back()->LowLink >= RootN->LowLink &&
454 "We cannot have a low link in an SCC lower than its root on the "
456 NewSCC->insert(*NodeStack.pop_back_val());
458 NewSCC->insert(*RootN);
460 // A final pass over all edges in the SCC (this remains linear as we only
461 // do this once when we build the SCC) to connect it to the parent sets of
463 bool IsLeafSCC = true;
464 for (Node *SCCN : NewSCC->Nodes)
465 for (Node &SCCChildN : *SCCN) {
466 SCC &ChildSCC = *SCCMap.lookup(&SCCChildN);
467 if (&ChildSCC == NewSCC)
469 ChildSCC.ParentSCCs.insert(NewSCC);
473 // For the SCCs where we fine no child SCCs, add them to the leaf list.
475 LeafSCCs.push_back(NewSCC);
480 LazyCallGraph::SCC *LazyCallGraph::getNextSCCInPostOrder() {
483 if (!DFSStack.empty()) {
484 N = DFSStack.back().first;
485 I = DFSStack.back().second;
488 // If we've handled all candidate entry nodes to the SCC forest, we're done.
490 if (SCCEntryNodes.empty())
493 N = &get(*SCCEntryNodes.pop_back_val());
494 } while (N->DFSNumber != 0);
496 N->LowLink = N->DFSNumber = 1;
501 assert(N->DFSNumber != 0 && "We should always assign a DFS number "
502 "before placing a node onto the stack.");
504 Node::iterator E = N->end();
507 if (ChildN.DFSNumber == 0) {
508 // Mark that we should start at this child when next this node is the
509 // top of the stack. We don't start at the next child to ensure this
510 // child's lowlink is reflected.
511 DFSStack.push_back(std::make_pair(N, N->begin()));
513 // Recurse onto this node via a tail call.
514 assert(!SCCMap.count(&ChildN) &&
515 "Found a node with 0 DFS number but already in an SCC!");
516 ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
523 // Track the lowest link of the childen, if any are still in the stack.
524 assert(ChildN.LowLink != 0 &&
525 "Low-link must not be zero with a non-zero DFS number.");
526 if (ChildN.LowLink >= 0 && ChildN.LowLink < N->LowLink)
527 N->LowLink = ChildN.LowLink;
531 if (N->LowLink == N->DFSNumber)
532 // Form the new SCC out of the top of the DFS stack.
533 return formSCC(N, PendingSCCStack);
535 // At this point we know that N cannot ever be an SCC root. Its low-link
536 // is not its dfs-number, and we've processed all of its children. It is
537 // just sitting here waiting until some node further down the stack gets
538 // low-link == dfs-number and pops it off as well. Move it to the pending
539 // stack which is pulled into the next SCC to be formed.
540 PendingSCCStack.push_back(N);
542 assert(!DFSStack.empty() && "We never found a viable root!");
543 N = DFSStack.back().first;
544 I = DFSStack.back().second;
549 char LazyCallGraphAnalysis::PassID;
551 LazyCallGraphPrinterPass::LazyCallGraphPrinterPass(raw_ostream &OS) : OS(OS) {}
553 static void printNodes(raw_ostream &OS, LazyCallGraph::Node &N,
554 SmallPtrSetImpl<LazyCallGraph::Node *> &Printed) {
555 // Recurse depth first through the nodes.
556 for (LazyCallGraph::Node &ChildN : N)
557 if (Printed.insert(&ChildN))
558 printNodes(OS, ChildN, Printed);
560 OS << " Call edges in function: " << N.getFunction().getName() << "\n";
561 for (LazyCallGraph::iterator I = N.begin(), E = N.end(); I != E; ++I)
562 OS << " -> " << I->getFunction().getName() << "\n";
567 static void printSCC(raw_ostream &OS, LazyCallGraph::SCC &SCC) {
568 ptrdiff_t SCCSize = std::distance(SCC.begin(), SCC.end());
569 OS << " SCC with " << SCCSize << " functions:\n";
571 for (LazyCallGraph::Node *N : SCC)
572 OS << " " << N->getFunction().getName() << "\n";
577 PreservedAnalyses LazyCallGraphPrinterPass::run(Module *M,
578 ModuleAnalysisManager *AM) {
579 LazyCallGraph &G = AM->getResult<LazyCallGraphAnalysis>(M);
581 OS << "Printing the call graph for module: " << M->getModuleIdentifier()
584 SmallPtrSet<LazyCallGraph::Node *, 16> Printed;
585 for (LazyCallGraph::Node &N : G)
586 if (Printed.insert(&N))
587 printNodes(OS, N, Printed);
589 for (LazyCallGraph::SCC &SCC : G.postorder_sccs())
592 return PreservedAnalyses::all();