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::LazyCallGraph(Module &M) : NextDFSNumber(0) {
70 if (!F.isDeclaration() && !F.hasLocalLinkage())
71 if (EntryNodeSet.insert(&F))
72 EntryNodes.push_back(&F);
74 // Now add entry nodes for functions reachable via initializers to globals.
75 SmallVector<Constant *, 16> Worklist;
76 SmallPtrSet<Constant *, 16> Visited;
77 for (GlobalVariable &GV : M.globals())
78 if (GV.hasInitializer())
79 if (Visited.insert(GV.getInitializer()))
80 Worklist.push_back(GV.getInitializer());
82 findCallees(Worklist, Visited, EntryNodes, EntryNodeSet);
84 for (auto &Entry : EntryNodes)
85 if (Function *F = Entry.dyn_cast<Function *>())
86 SCCEntryNodes.insert(F);
88 SCCEntryNodes.insert(&Entry.get<Node *>()->getFunction());
91 LazyCallGraph::LazyCallGraph(LazyCallGraph &&G)
92 : BPA(std::move(G.BPA)), NodeMap(std::move(G.NodeMap)),
93 EntryNodes(std::move(G.EntryNodes)),
94 EntryNodeSet(std::move(G.EntryNodeSet)), SCCBPA(std::move(G.SCCBPA)),
95 SCCMap(std::move(G.SCCMap)), LeafSCCs(std::move(G.LeafSCCs)),
96 DFSStack(std::move(G.DFSStack)),
97 SCCEntryNodes(std::move(G.SCCEntryNodes)),
98 NextDFSNumber(G.NextDFSNumber) {
102 LazyCallGraph &LazyCallGraph::operator=(LazyCallGraph &&G) {
103 BPA = std::move(G.BPA);
104 NodeMap = std::move(G.NodeMap);
105 EntryNodes = std::move(G.EntryNodes);
106 EntryNodeSet = std::move(G.EntryNodeSet);
107 SCCBPA = std::move(G.SCCBPA);
108 SCCMap = std::move(G.SCCMap);
109 LeafSCCs = std::move(G.LeafSCCs);
110 DFSStack = std::move(G.DFSStack);
111 SCCEntryNodes = std::move(G.SCCEntryNodes);
112 NextDFSNumber = G.NextDFSNumber;
117 LazyCallGraph::Node *LazyCallGraph::insertInto(Function &F, Node *&MappedN) {
118 return new (MappedN = BPA.Allocate()) Node(*this, F);
121 void LazyCallGraph::updateGraphPtrs() {
122 // Process all nodes updating the graph pointers.
123 SmallVector<Node *, 16> Worklist;
124 for (auto &Entry : EntryNodes)
125 if (Node *EntryN = Entry.dyn_cast<Node *>())
126 Worklist.push_back(EntryN);
128 while (!Worklist.empty()) {
129 Node *N = Worklist.pop_back_val();
131 for (auto &Callee : N->Callees)
132 if (Node *CalleeN = Callee.dyn_cast<Node *>())
133 Worklist.push_back(CalleeN);
137 LazyCallGraph::SCC *LazyCallGraph::getNextSCCInPostOrder() {
138 // When the stack is empty, there are no more SCCs to walk in this graph.
139 if (DFSStack.empty()) {
140 // If we've handled all candidate entry nodes to the SCC forest, we're done.
141 if (SCCEntryNodes.empty())
144 Node *N = get(*SCCEntryNodes.pop_back_val());
145 DFSStack.push_back(std::make_pair(N, N->begin()));
148 Node *N = DFSStack.back().first;
149 if (N->DFSNumber == 0) {
150 // This node hasn't been visited before, assign it a DFS number and remove
151 // it from the entry set.
152 N->LowLink = N->DFSNumber = NextDFSNumber++;
153 SCCEntryNodes.remove(&N->getFunction());
156 for (auto I = DFSStack.back().second, E = N->end(); I != E; ++I) {
158 if (ChildN->DFSNumber == 0) {
159 // Mark that we should start at this child when next this node is the
160 // top of the stack. We don't start at the next child to ensure this
161 // child's lowlink is reflected.
162 // FIXME: I don't actually think this is required, and we could start
163 // at the next child.
164 DFSStack.back().second = I;
166 // Recurse onto this node via a tail call.
167 DFSStack.push_back(std::make_pair(ChildN, ChildN->begin()));
168 return LazyCallGraph::getNextSCCInPostOrder();
171 // Track the lowest link of the childen, if any are still in the stack.
172 if (ChildN->LowLink < N->LowLink && !SCCMap.count(&ChildN->getFunction()))
173 N->LowLink = ChildN->LowLink;
176 // The tail of the stack is the new SCC. Allocate the SCC and pop the stack
178 SCC *NewSCC = new (SCCBPA.Allocate()) SCC();
180 // Because we don't follow the strict Tarjan recursive formulation, walk
181 // from the top of the stack down, propagating the lowest link and stopping
182 // when the DFS number is the lowest link.
183 int LowestLink = N->LowLink;
185 Node *SCCN = DFSStack.pop_back_val().first;
186 SCCMap.insert(std::make_pair(&SCCN->getFunction(), NewSCC));
187 NewSCC->Nodes.push_back(SCCN);
188 LowestLink = std::min(LowestLink, SCCN->LowLink);
190 NewSCC->NodeSet.insert(&SCCN->getFunction());
192 assert(Inserted && "Cannot have duplicates in the DFSStack!");
193 } while (!DFSStack.empty() && LowestLink <= DFSStack.back().first->DFSNumber);
194 assert(LowestLink == NewSCC->Nodes.back()->DFSNumber &&
195 "Cannot stop with a DFS number greater than the lowest link!");
197 // A final pass over all edges in the SCC (this remains linear as we only
198 // do this once when we build the SCC) to connect it to the parent sets of
200 bool IsLeafSCC = true;
201 for (Node *SCCN : NewSCC->Nodes)
202 for (Node *SCCChildN : *SCCN) {
203 if (NewSCC->NodeSet.count(&SCCChildN->getFunction()))
205 SCC *ChildSCC = SCCMap.lookup(&SCCChildN->getFunction());
207 "Must have all child SCCs processed when building a new SCC!");
208 ChildSCC->ParentSCCs.insert(NewSCC);
212 // For the SCCs where we fine no child SCCs, add them to the leaf list.
214 LeafSCCs.push_back(NewSCC);
219 char LazyCallGraphAnalysis::PassID;
221 LazyCallGraphPrinterPass::LazyCallGraphPrinterPass(raw_ostream &OS) : OS(OS) {}
223 static void printNodes(raw_ostream &OS, LazyCallGraph::Node &N,
224 SmallPtrSetImpl<LazyCallGraph::Node *> &Printed) {
225 // Recurse depth first through the nodes.
226 for (LazyCallGraph::Node *ChildN : N)
227 if (Printed.insert(ChildN))
228 printNodes(OS, *ChildN, Printed);
230 OS << " Call edges in function: " << N.getFunction().getName() << "\n";
231 for (LazyCallGraph::iterator I = N.begin(), E = N.end(); I != E; ++I)
232 OS << " -> " << I->getFunction().getName() << "\n";
237 static void printSCC(raw_ostream &OS, LazyCallGraph::SCC &SCC) {
238 ptrdiff_t SCCSize = std::distance(SCC.begin(), SCC.end());
239 OS << " SCC with " << SCCSize << " functions:\n";
241 for (LazyCallGraph::Node *N : SCC)
242 OS << " " << N->getFunction().getName() << "\n";
247 PreservedAnalyses LazyCallGraphPrinterPass::run(Module *M,
248 ModuleAnalysisManager *AM) {
249 LazyCallGraph &G = AM->getResult<LazyCallGraphAnalysis>(M);
251 OS << "Printing the call graph for module: " << M->getModuleIdentifier()
254 SmallPtrSet<LazyCallGraph::Node *, 16> Printed;
255 for (LazyCallGraph::Node *N : G)
256 if (Printed.insert(N))
257 printNodes(OS, *N, Printed);
259 for (LazyCallGraph::SCC *SCC : G.postorder_sccs())
262 return PreservedAnalyses::all();