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 void LazyCallGraph::SCC::insertIntraSCCEdge(Node &CallerN, Node &CalleeN) {
166 // First insert it into the caller.
167 CallerN.insertEdgeInternal(CalleeN);
169 assert(G->SCCMap.lookup(&CallerN) == this && "Caller must be in this SCC.");
170 assert(G->SCCMap.lookup(&CalleeN) == this && "Callee must be in this SCC.");
172 // Nothing changes about this SCC or any other.
175 void LazyCallGraph::SCC::removeInterSCCEdge(Node &CallerN, Node &CalleeN) {
176 // First remove it from the node.
177 CallerN.removeEdgeInternal(CalleeN.getFunction());
179 assert(G->SCCMap.lookup(&CallerN) == this &&
180 "The caller must be a member of this SCC.");
182 SCC &CalleeC = *G->SCCMap.lookup(&CalleeN);
183 assert(&CalleeC != this &&
184 "This API only supports the rmoval of inter-SCC edges.");
186 assert(std::find(G->LeafSCCs.begin(), G->LeafSCCs.end(), this) ==
188 "Cannot have a leaf SCC caller with a different SCC callee.");
190 bool HasOtherCallToCalleeC = false;
191 bool HasOtherCallOutsideSCC = false;
192 for (Node *N : *this) {
193 for (Node &OtherCalleeN : *N) {
194 SCC &OtherCalleeC = *G->SCCMap.lookup(&OtherCalleeN);
195 if (&OtherCalleeC == &CalleeC) {
196 HasOtherCallToCalleeC = true;
199 if (&OtherCalleeC != this)
200 HasOtherCallOutsideSCC = true;
202 if (HasOtherCallToCalleeC)
205 // Because the SCCs form a DAG, deleting such an edge cannot change the set
206 // of SCCs in the graph. However, it may cut an edge of the SCC DAG, making
207 // the caller no longer a parent of the callee. Walk the other call edges
208 // in the caller to tell.
209 if (!HasOtherCallToCalleeC) {
210 bool Removed = CalleeC.ParentSCCs.erase(this);
213 "Did not find the caller SCC in the callee SCC's parent list!");
215 // It may orphan an SCC if it is the last edge reaching it, but that does
216 // not violate any invariants of the graph.
217 if (CalleeC.ParentSCCs.empty())
218 DEBUG(dbgs() << "LCG: Update removing " << CallerN.getFunction().getName()
219 << " -> " << CalleeN.getFunction().getName()
220 << " edge orphaned the callee's SCC!\n");
223 // It may make the Caller SCC a leaf SCC.
224 if (!HasOtherCallOutsideSCC)
225 G->LeafSCCs.push_back(this);
228 void LazyCallGraph::SCC::internalDFS(
229 SmallVectorImpl<std::pair<Node *, Node::iterator>> &DFSStack,
230 SmallVectorImpl<Node *> &PendingSCCStack, Node *N,
231 SmallVectorImpl<SCC *> &ResultSCCs) {
232 Node::iterator I = N->begin();
233 N->LowLink = N->DFSNumber = 1;
234 int NextDFSNumber = 2;
236 assert(N->DFSNumber != 0 && "We should always assign a DFS number "
237 "before processing a node.");
239 // We simulate recursion by popping out of the nested loop and continuing.
240 Node::iterator E = N->end();
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) {
249 while (!PendingSCCStack.empty())
250 insert(*PendingSCCStack.pop_back_val());
251 while (!DFSStack.empty())
252 insert(*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);
263 if (ChildN.DFSNumber == 0) {
264 // Mark that we should start at this child when next this node is the
265 // top of the stack. We don't start at the next child to ensure this
266 // child's lowlink is reflected.
267 DFSStack.push_back(std::make_pair(N, I));
269 // Continue, resetting to the child node.
270 ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
277 // Track the lowest link of the childen, if any are still in the stack.
278 // Any child not on the stack will have a LowLink of -1.
279 assert(ChildN.LowLink != 0 &&
280 "Low-link must not be zero with a non-zero DFS number.");
281 if (ChildN.LowLink >= 0 && ChildN.LowLink < N->LowLink)
282 N->LowLink = ChildN.LowLink;
286 if (N->LowLink == N->DFSNumber) {
287 ResultSCCs.push_back(G->formSCC(N, PendingSCCStack));
288 if (DFSStack.empty())
291 // At this point we know that N cannot ever be an SCC root. Its low-link
292 // is not its dfs-number, and we've processed all of its children. It is
293 // just sitting here waiting until some node further down the stack gets
294 // low-link == dfs-number and pops it off as well. Move it to the pending
295 // stack which is pulled into the next SCC to be formed.
296 PendingSCCStack.push_back(N);
298 assert(!DFSStack.empty() && "We shouldn't have an empty stack!");
301 N = DFSStack.back().first;
302 I = DFSStack.back().second;
307 SmallVector<LazyCallGraph::SCC *, 1>
308 LazyCallGraph::SCC::removeIntraSCCEdge(Node &CallerN,
310 // First remove it from the node.
311 CallerN.removeEdgeInternal(CalleeN.getFunction());
313 // We return a list of the resulting *new* SCCs in postorder.
314 SmallVector<SCC *, 1> ResultSCCs;
316 // Direct recursion doesn't impact the SCC graph at all.
317 if (&CallerN == &CalleeN)
320 // The worklist is every node in the original SCC.
321 SmallVector<Node *, 1> Worklist;
322 Worklist.swap(Nodes);
323 for (Node *N : Worklist) {
324 // The nodes formerly in this SCC are no longer in any SCC.
329 assert(Worklist.size() > 1 && "We have to have at least two nodes to have an "
330 "edge between them that is within the SCC.");
332 // The callee can already reach every node in this SCC (by definition). It is
333 // the only node we know will stay inside this SCC. Everything which
334 // transitively reaches Callee will also remain in the SCC. To model this we
335 // incrementally add any chain of nodes which reaches something in the new
336 // node set to the new node set. This short circuits one side of the Tarjan's
340 // We're going to do a full mini-Tarjan's walk using a local stack here.
341 SmallVector<std::pair<Node *, Node::iterator>, 4> DFSStack;
342 SmallVector<Node *, 4> PendingSCCStack;
344 Node *N = Worklist.pop_back_val();
345 if (N->DFSNumber == 0)
346 internalDFS(DFSStack, PendingSCCStack, N, ResultSCCs);
348 assert(DFSStack.empty() && "Didn't flush the entire DFS stack!");
349 assert(PendingSCCStack.empty() && "Didn't flush all pending SCC nodes!");
350 } while (!Worklist.empty());
352 // Now we need to reconnect the current SCC to the graph.
353 bool IsLeafSCC = true;
354 for (Node *N : Nodes) {
355 for (Node &ChildN : *N) {
356 SCC &ChildSCC = *G->SCCMap.lookup(&ChildN);
357 if (&ChildSCC == this)
359 ChildSCC.ParentSCCs.insert(this);
364 if (!ResultSCCs.empty())
365 assert(!IsLeafSCC && "This SCC cannot be a leaf as we have split out new "
366 "SCCs by removing this edge.");
367 if (!std::any_of(G->LeafSCCs.begin(), G->LeafSCCs.end(),
368 [&](SCC *C) { return C == this; }))
369 assert(!IsLeafSCC && "This SCC cannot be a leaf as it already had child "
370 "SCCs before we removed this edge.");
372 // If this SCC stopped being a leaf through this edge removal, remove it from
373 // the leaf SCC list.
374 if (!IsLeafSCC && !ResultSCCs.empty())
375 G->LeafSCCs.erase(std::remove(G->LeafSCCs.begin(), G->LeafSCCs.end(), this),
378 // Return the new list of SCCs.
382 void LazyCallGraph::insertEdge(Node &CallerN, Function &Callee) {
383 assert(SCCMap.empty() && DFSStack.empty() &&
384 "This method cannot be called after SCCs have been formed!");
386 return CallerN.insertEdgeInternal(Callee);
389 void LazyCallGraph::removeEdge(Node &CallerN, Function &Callee) {
390 assert(SCCMap.empty() && DFSStack.empty() &&
391 "This method cannot be called after SCCs have been formed!");
393 return CallerN.removeEdgeInternal(Callee);
396 LazyCallGraph::Node &LazyCallGraph::insertInto(Function &F, Node *&MappedN) {
397 return *new (MappedN = BPA.Allocate()) Node(*this, F);
400 void LazyCallGraph::updateGraphPtrs() {
401 // Process all nodes updating the graph pointers.
403 SmallVector<Node *, 16> Worklist;
404 for (auto &Entry : EntryNodes)
405 if (Node *EntryN = Entry.dyn_cast<Node *>())
406 Worklist.push_back(EntryN);
408 while (!Worklist.empty()) {
409 Node *N = Worklist.pop_back_val();
411 for (auto &Callee : N->Callees)
412 if (!Callee.isNull())
413 if (Node *CalleeN = Callee.dyn_cast<Node *>())
414 Worklist.push_back(CalleeN);
418 // Process all SCCs updating the graph pointers.
420 SmallVector<SCC *, 16> Worklist(LeafSCCs.begin(), LeafSCCs.end());
422 while (!Worklist.empty()) {
423 SCC *C = Worklist.pop_back_val();
425 Worklist.insert(Worklist.end(), C->ParentSCCs.begin(),
426 C->ParentSCCs.end());
431 LazyCallGraph::SCC *LazyCallGraph::formSCC(Node *RootN,
432 SmallVectorImpl<Node *> &NodeStack) {
433 // The tail of the stack is the new SCC. Allocate the SCC and pop the stack
435 SCC *NewSCC = new (SCCBPA.Allocate()) SCC(*this);
437 while (!NodeStack.empty() && NodeStack.back()->DFSNumber > RootN->DFSNumber) {
438 assert(NodeStack.back()->LowLink >= RootN->LowLink &&
439 "We cannot have a low link in an SCC lower than its root on the "
441 NewSCC->insert(*NodeStack.pop_back_val());
443 NewSCC->insert(*RootN);
445 // A final pass over all edges in the SCC (this remains linear as we only
446 // do this once when we build the SCC) to connect it to the parent sets of
448 bool IsLeafSCC = true;
449 for (Node *SCCN : NewSCC->Nodes)
450 for (Node &SCCChildN : *SCCN) {
451 if (SCCMap.lookup(&SCCChildN) == NewSCC)
453 SCC &ChildSCC = *SCCMap.lookup(&SCCChildN);
454 ChildSCC.ParentSCCs.insert(NewSCC);
458 // For the SCCs where we fine no child SCCs, add them to the leaf list.
460 LeafSCCs.push_back(NewSCC);
465 LazyCallGraph::SCC *LazyCallGraph::getNextSCCInPostOrder() {
468 if (!DFSStack.empty()) {
469 N = DFSStack.back().first;
470 I = DFSStack.back().second;
473 // If we've handled all candidate entry nodes to the SCC forest, we're done.
475 if (SCCEntryNodes.empty())
478 N = &get(*SCCEntryNodes.pop_back_val());
479 } while (N->DFSNumber != 0);
481 N->LowLink = N->DFSNumber = 1;
486 assert(N->DFSNumber != 0 && "We should always assign a DFS number "
487 "before placing a node onto the stack.");
489 Node::iterator E = N->end();
492 if (ChildN.DFSNumber == 0) {
493 // Mark that we should start at this child when next this node is the
494 // top of the stack. We don't start at the next child to ensure this
495 // child's lowlink is reflected.
496 DFSStack.push_back(std::make_pair(N, N->begin()));
498 // Recurse onto this node via a tail call.
499 assert(!SCCMap.count(&ChildN) &&
500 "Found a node with 0 DFS number but already in an SCC!");
501 ChildN.LowLink = ChildN.DFSNumber = NextDFSNumber++;
508 // Track the lowest link of the childen, if any are still in the stack.
509 assert(ChildN.LowLink != 0 &&
510 "Low-link must not be zero with a non-zero DFS number.");
511 if (ChildN.LowLink >= 0 && ChildN.LowLink < N->LowLink)
512 N->LowLink = ChildN.LowLink;
516 if (N->LowLink == N->DFSNumber)
517 // Form the new SCC out of the top of the DFS stack.
518 return formSCC(N, PendingSCCStack);
520 // At this point we know that N cannot ever be an SCC root. Its low-link
521 // is not its dfs-number, and we've processed all of its children. It is
522 // just sitting here waiting until some node further down the stack gets
523 // low-link == dfs-number and pops it off as well. Move it to the pending
524 // stack which is pulled into the next SCC to be formed.
525 PendingSCCStack.push_back(N);
527 assert(!DFSStack.empty() && "We never found a viable root!");
528 N = DFSStack.back().first;
529 I = DFSStack.back().second;
534 char LazyCallGraphAnalysis::PassID;
536 LazyCallGraphPrinterPass::LazyCallGraphPrinterPass(raw_ostream &OS) : OS(OS) {}
538 static void printNodes(raw_ostream &OS, LazyCallGraph::Node &N,
539 SmallPtrSetImpl<LazyCallGraph::Node *> &Printed) {
540 // Recurse depth first through the nodes.
541 for (LazyCallGraph::Node &ChildN : N)
542 if (Printed.insert(&ChildN))
543 printNodes(OS, ChildN, Printed);
545 OS << " Call edges in function: " << N.getFunction().getName() << "\n";
546 for (LazyCallGraph::iterator I = N.begin(), E = N.end(); I != E; ++I)
547 OS << " -> " << I->getFunction().getName() << "\n";
552 static void printSCC(raw_ostream &OS, LazyCallGraph::SCC &SCC) {
553 ptrdiff_t SCCSize = std::distance(SCC.begin(), SCC.end());
554 OS << " SCC with " << SCCSize << " functions:\n";
556 for (LazyCallGraph::Node *N : SCC)
557 OS << " " << N->getFunction().getName() << "\n";
562 PreservedAnalyses LazyCallGraphPrinterPass::run(Module *M,
563 ModuleAnalysisManager *AM) {
564 LazyCallGraph &G = AM->getResult<LazyCallGraphAnalysis>(M);
566 OS << "Printing the call graph for module: " << M->getModuleIdentifier()
569 SmallPtrSet<LazyCallGraph::Node *, 16> Printed;
570 for (LazyCallGraph::Node &N : G)
571 if (Printed.insert(&N))
572 printNodes(OS, N, Printed);
574 for (LazyCallGraph::SCC &SCC : G.postorder_sccs())
577 return PreservedAnalyses::all();