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/raw_ostream.h"
20 static void findCallees(
21 SmallVectorImpl<Constant *> &Worklist, SmallPtrSetImpl<Constant *> &Visited,
22 SmallVectorImpl<PointerUnion<Function *, LazyCallGraph::Node *>> &Callees,
23 SmallPtrSetImpl<Function *> &CalleeSet) {
24 while (!Worklist.empty()) {
25 Constant *C = Worklist.pop_back_val();
27 if (Function *F = dyn_cast<Function>(C)) {
28 // Note that we consider *any* function with a definition to be a viable
29 // edge. Even if the function's definition is subject to replacement by
30 // some other module (say, a weak definition) there may still be
31 // optimizations which essentially speculate based on the definition and
32 // a way to check that the specific definition is in fact the one being
33 // used. For example, this could be done by moving the weak definition to
34 // a strong (internal) definition and making the weak definition be an
35 // alias. Then a test of the address of the weak function against the new
36 // strong definition's address would be an effective way to determine the
37 // safety of optimizing a direct call edge.
38 if (!F->isDeclaration() && CalleeSet.insert(F))
43 for (Value *Op : C->operand_values())
44 if (Visited.insert(cast<Constant>(Op)))
45 Worklist.push_back(cast<Constant>(Op));
49 LazyCallGraph::Node::Node(LazyCallGraph &G, Function &F)
50 : G(&G), F(F), DFSNumber(0), LowLink(0) {
51 SmallVector<Constant *, 16> Worklist;
52 SmallPtrSet<Constant *, 16> Visited;
53 // Find all the potential callees in this function. First walk the
54 // instructions and add every operand which is a constant to the worklist.
55 for (BasicBlock &BB : F)
56 for (Instruction &I : BB)
57 for (Value *Op : I.operand_values())
58 if (Constant *C = dyn_cast<Constant>(Op))
59 if (Visited.insert(C))
60 Worklist.push_back(C);
62 // We've collected all the constant (and thus potentially function or
63 // function containing) operands to all of the instructions in the function.
64 // Process them (recursively) collecting every function found.
65 findCallees(Worklist, Visited, Callees, CalleeSet);
68 LazyCallGraph::Node::Node(LazyCallGraph &G, const Node &OtherN)
69 : G(&G), F(OtherN.F), DFSNumber(0), LowLink(0), CalleeSet(OtherN.CalleeSet) {
70 // Loop over the other node's callees, adding the Function*s to our list
71 // directly, and recursing to add the Node*s.
72 Callees.reserve(OtherN.Callees.size());
73 for (const auto &OtherCallee : OtherN.Callees)
74 if (Function *Callee = OtherCallee.dyn_cast<Function *>())
75 Callees.push_back(Callee);
77 Callees.push_back(G.copyInto(*OtherCallee.get<Node *>()));
80 LazyCallGraph::LazyCallGraph(Module &M) {
82 if (!F.isDeclaration() && !F.hasLocalLinkage())
83 if (EntryNodeSet.insert(&F))
84 EntryNodes.push_back(&F);
86 // Now add entry nodes for functions reachable via initializers to globals.
87 SmallVector<Constant *, 16> Worklist;
88 SmallPtrSet<Constant *, 16> Visited;
89 for (GlobalVariable &GV : M.globals())
90 if (GV.hasInitializer())
91 if (Visited.insert(GV.getInitializer()))
92 Worklist.push_back(GV.getInitializer());
94 findCallees(Worklist, Visited, EntryNodes, EntryNodeSet);
96 for (auto &Entry : EntryNodes)
97 if (Function *F = Entry.dyn_cast<Function *>())
98 SCCEntryNodes.insert(F);
100 SCCEntryNodes.insert(&Entry.get<Node *>()->getFunction());
103 LazyCallGraph::LazyCallGraph(const LazyCallGraph &G)
104 : EntryNodeSet(G.EntryNodeSet) {
105 EntryNodes.reserve(G.EntryNodes.size());
106 for (const auto &EntryNode : G.EntryNodes)
107 if (Function *Callee = EntryNode.dyn_cast<Function *>())
108 EntryNodes.push_back(Callee);
110 EntryNodes.push_back(copyInto(*EntryNode.get<Node *>()));
112 // Just re-populate the SCCEntryNodes structure so we recompute the SCCs if
114 for (auto &Entry : EntryNodes)
115 if (Function *F = Entry.dyn_cast<Function *>())
116 SCCEntryNodes.insert(F);
118 SCCEntryNodes.insert(&Entry.get<Node *>()->getFunction());
121 LazyCallGraph::LazyCallGraph(LazyCallGraph &&G)
122 : BPA(std::move(G.BPA)), EntryNodes(std::move(G.EntryNodes)),
123 EntryNodeSet(std::move(G.EntryNodeSet)), SCCBPA(std::move(G.SCCBPA)),
124 SCCMap(std::move(G.SCCMap)), LeafSCCs(std::move(G.LeafSCCs)),
125 DFSStack(std::move(G.DFSStack)),
126 SCCEntryNodes(std::move(G.SCCEntryNodes)) {
127 // Process all nodes updating the graph pointers.
128 SmallVector<Node *, 16> Worklist;
129 for (auto &Entry : EntryNodes)
130 if (Node *EntryN = Entry.dyn_cast<Node *>())
131 Worklist.push_back(EntryN);
133 while (!Worklist.empty()) {
134 Node *N = Worklist.pop_back_val();
136 for (auto &Callee : N->Callees)
137 if (Node *CalleeN = Callee.dyn_cast<Node *>())
138 Worklist.push_back(CalleeN);
142 LazyCallGraph::Node *LazyCallGraph::insertInto(Function &F, Node *&MappedN) {
143 return new (MappedN = BPA.Allocate()) Node(*this, F);
146 LazyCallGraph::Node *LazyCallGraph::copyInto(const Node &OtherN) {
147 Node *&N = NodeMap[&OtherN.F];
151 return new (N = BPA.Allocate()) Node(*this, OtherN);
154 LazyCallGraph::SCC *LazyCallGraph::getNextSCCInPostOrder() {
155 // When the stack is empty, there are no more SCCs to walk in this graph.
156 if (DFSStack.empty()) {
157 // If we've handled all candidate entry nodes to the SCC forest, we're done.
158 if (SCCEntryNodes.empty())
161 Node *N = get(*SCCEntryNodes.pop_back_val());
162 DFSStack.push_back(std::make_pair(N, N->begin()));
165 Node *N = DFSStack.back().first;
166 if (N->DFSNumber == 0) {
167 // This node hasn't been visited before, assign it a DFS number and remove
168 // it from the entry set.
169 N->LowLink = N->DFSNumber = NextDFSNumber++;
170 SCCEntryNodes.remove(&N->getFunction());
173 for (auto I = DFSStack.back().second, E = N->end(); I != E; ++I) {
175 if (ChildN->DFSNumber == 0) {
176 // Mark that we should start at this child when next this node is the
177 // top of the stack. We don't start at the next child to ensure this
178 // child's lowlink is reflected.
179 // FIXME: I don't actually think this is required, and we could start
180 // at the next child.
181 DFSStack.back().second = I;
183 // Recurse onto this node via a tail call.
184 DFSStack.push_back(std::make_pair(ChildN, ChildN->begin()));
185 return LazyCallGraph::getNextSCCInPostOrder();
188 // Track the lowest link of the childen, if any are still in the stack.
189 if (ChildN->LowLink < N->LowLink && !SCCMap.count(&ChildN->getFunction()))
190 N->LowLink = ChildN->LowLink;
193 // The tail of the stack is the new SCC. Allocate the SCC and pop the stack
195 SCC *NewSCC = new (SCCBPA.Allocate()) SCC();
197 // Because we don't follow the strict Tarjan recursive formulation, walk
198 // from the top of the stack down, propagating the lowest link and stopping
199 // when the DFS number is the lowest link.
200 int LowestLink = N->LowLink;
202 Node *SCCN = DFSStack.pop_back_val().first;
203 SCCMap.insert(std::make_pair(&SCCN->getFunction(), NewSCC));
204 NewSCC->Nodes.push_back(SCCN);
205 LowestLink = std::min(LowestLink, SCCN->LowLink);
207 NewSCC->NodeSet.insert(&SCCN->getFunction());
209 assert(Inserted && "Cannot have duplicates in the DFSStack!");
210 } while (!DFSStack.empty() && LowestLink <= DFSStack.back().first->DFSNumber);
211 assert(LowestLink == NewSCC->Nodes.back()->DFSNumber &&
212 "Cannot stop with a DFS number greater than the lowest link!");
214 // A final pass over all edges in the SCC (this remains linear as we only
215 // do this once when we build the SCC) to connect it to the parent sets of
217 bool IsLeafSCC = true;
218 for (Node *SCCN : NewSCC->Nodes)
219 for (Node *SCCChildN : *SCCN) {
220 if (NewSCC->NodeSet.count(&SCCChildN->getFunction()))
222 SCC *ChildSCC = SCCMap.lookup(&SCCChildN->getFunction());
224 "Must have all child SCCs processed when building a new SCC!");
225 ChildSCC->ParentSCCs.insert(NewSCC);
229 // For the SCCs where we fine no child SCCs, add them to the leaf list.
231 LeafSCCs.push_back(NewSCC);
236 char LazyCallGraphAnalysis::PassID;
238 LazyCallGraphPrinterPass::LazyCallGraphPrinterPass(raw_ostream &OS) : OS(OS) {}
240 static void printNodes(raw_ostream &OS, LazyCallGraph::Node &N,
241 SmallPtrSetImpl<LazyCallGraph::Node *> &Printed) {
242 // Recurse depth first through the nodes.
243 for (LazyCallGraph::Node *ChildN : N)
244 if (Printed.insert(ChildN))
245 printNodes(OS, *ChildN, Printed);
247 OS << " Call edges in function: " << N.getFunction().getName() << "\n";
248 for (LazyCallGraph::iterator I = N.begin(), E = N.end(); I != E; ++I)
249 OS << " -> " << I->getFunction().getName() << "\n";
254 static void printSCC(raw_ostream &OS, LazyCallGraph::SCC &SCC) {
255 ptrdiff_t SCCSize = std::distance(SCC.begin(), SCC.end());
256 OS << " SCC with " << SCCSize << " functions:\n";
258 for (LazyCallGraph::Node *N : SCC)
259 OS << " " << N->getFunction().getName() << "\n";
264 PreservedAnalyses LazyCallGraphPrinterPass::run(Module *M,
265 ModuleAnalysisManager *AM) {
266 LazyCallGraph &G = AM->getResult<LazyCallGraphAnalysis>(M);
268 OS << "Printing the call graph for module: " << M->getModuleIdentifier()
271 SmallPtrSet<LazyCallGraph::Node *, 16> Printed;
272 for (LazyCallGraph::Node *N : G)
273 if (Printed.insert(N))
274 printNodes(OS, *N, Printed);
276 for (LazyCallGraph::SCC *SCC : G.postorder_sccs())
279 return PreservedAnalyses::all();