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) {
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)), EntryNodes(std::move(G.EntryNodes)),
93 EntryNodeSet(std::move(G.EntryNodeSet)), SCCBPA(std::move(G.SCCBPA)),
94 SCCMap(std::move(G.SCCMap)), LeafSCCs(std::move(G.LeafSCCs)),
95 DFSStack(std::move(G.DFSStack)),
96 SCCEntryNodes(std::move(G.SCCEntryNodes)) {
100 LazyCallGraph &LazyCallGraph::operator=(LazyCallGraph &&G) {
101 BPA = std::move(G.BPA);
102 EntryNodes = std::move(G.EntryNodes);
103 EntryNodeSet = std::move(G.EntryNodeSet);
104 SCCBPA = std::move(G.SCCBPA);
105 SCCMap = std::move(G.SCCMap);
106 LeafSCCs = std::move(G.LeafSCCs);
107 DFSStack = std::move(G.DFSStack);
108 SCCEntryNodes = std::move(G.SCCEntryNodes);
113 LazyCallGraph::Node *LazyCallGraph::insertInto(Function &F, Node *&MappedN) {
114 return new (MappedN = BPA.Allocate()) Node(*this, F);
117 void LazyCallGraph::updateGraphPtrs() {
118 // Process all nodes updating the graph pointers.
119 SmallVector<Node *, 16> Worklist;
120 for (auto &Entry : EntryNodes)
121 if (Node *EntryN = Entry.dyn_cast<Node *>())
122 Worklist.push_back(EntryN);
124 while (!Worklist.empty()) {
125 Node *N = Worklist.pop_back_val();
127 for (auto &Callee : N->Callees)
128 if (Node *CalleeN = Callee.dyn_cast<Node *>())
129 Worklist.push_back(CalleeN);
133 LazyCallGraph::SCC *LazyCallGraph::getNextSCCInPostOrder() {
134 // When the stack is empty, there are no more SCCs to walk in this graph.
135 if (DFSStack.empty()) {
136 // If we've handled all candidate entry nodes to the SCC forest, we're done.
137 if (SCCEntryNodes.empty())
140 Node *N = get(*SCCEntryNodes.pop_back_val());
141 DFSStack.push_back(std::make_pair(N, N->begin()));
144 Node *N = DFSStack.back().first;
145 if (N->DFSNumber == 0) {
146 // This node hasn't been visited before, assign it a DFS number and remove
147 // it from the entry set.
148 N->LowLink = N->DFSNumber = NextDFSNumber++;
149 SCCEntryNodes.remove(&N->getFunction());
152 for (auto I = DFSStack.back().second, E = N->end(); I != E; ++I) {
154 if (ChildN->DFSNumber == 0) {
155 // Mark that we should start at this child when next this node is the
156 // top of the stack. We don't start at the next child to ensure this
157 // child's lowlink is reflected.
158 // FIXME: I don't actually think this is required, and we could start
159 // at the next child.
160 DFSStack.back().second = I;
162 // Recurse onto this node via a tail call.
163 DFSStack.push_back(std::make_pair(ChildN, ChildN->begin()));
164 return LazyCallGraph::getNextSCCInPostOrder();
167 // Track the lowest link of the childen, if any are still in the stack.
168 if (ChildN->LowLink < N->LowLink && !SCCMap.count(&ChildN->getFunction()))
169 N->LowLink = ChildN->LowLink;
172 // The tail of the stack is the new SCC. Allocate the SCC and pop the stack
174 SCC *NewSCC = new (SCCBPA.Allocate()) SCC();
176 // Because we don't follow the strict Tarjan recursive formulation, walk
177 // from the top of the stack down, propagating the lowest link and stopping
178 // when the DFS number is the lowest link.
179 int LowestLink = N->LowLink;
181 Node *SCCN = DFSStack.pop_back_val().first;
182 SCCMap.insert(std::make_pair(&SCCN->getFunction(), NewSCC));
183 NewSCC->Nodes.push_back(SCCN);
184 LowestLink = std::min(LowestLink, SCCN->LowLink);
186 NewSCC->NodeSet.insert(&SCCN->getFunction());
188 assert(Inserted && "Cannot have duplicates in the DFSStack!");
189 } while (!DFSStack.empty() && LowestLink <= DFSStack.back().first->DFSNumber);
190 assert(LowestLink == NewSCC->Nodes.back()->DFSNumber &&
191 "Cannot stop with a DFS number greater than the lowest link!");
193 // A final pass over all edges in the SCC (this remains linear as we only
194 // do this once when we build the SCC) to connect it to the parent sets of
196 bool IsLeafSCC = true;
197 for (Node *SCCN : NewSCC->Nodes)
198 for (Node *SCCChildN : *SCCN) {
199 if (NewSCC->NodeSet.count(&SCCChildN->getFunction()))
201 SCC *ChildSCC = SCCMap.lookup(&SCCChildN->getFunction());
203 "Must have all child SCCs processed when building a new SCC!");
204 ChildSCC->ParentSCCs.insert(NewSCC);
208 // For the SCCs where we fine no child SCCs, add them to the leaf list.
210 LeafSCCs.push_back(NewSCC);
215 char LazyCallGraphAnalysis::PassID;
217 LazyCallGraphPrinterPass::LazyCallGraphPrinterPass(raw_ostream &OS) : OS(OS) {}
219 static void printNodes(raw_ostream &OS, LazyCallGraph::Node &N,
220 SmallPtrSetImpl<LazyCallGraph::Node *> &Printed) {
221 // Recurse depth first through the nodes.
222 for (LazyCallGraph::Node *ChildN : N)
223 if (Printed.insert(ChildN))
224 printNodes(OS, *ChildN, Printed);
226 OS << " Call edges in function: " << N.getFunction().getName() << "\n";
227 for (LazyCallGraph::iterator I = N.begin(), E = N.end(); I != E; ++I)
228 OS << " -> " << I->getFunction().getName() << "\n";
233 static void printSCC(raw_ostream &OS, LazyCallGraph::SCC &SCC) {
234 ptrdiff_t SCCSize = std::distance(SCC.begin(), SCC.end());
235 OS << " SCC with " << SCCSize << " functions:\n";
237 for (LazyCallGraph::Node *N : SCC)
238 OS << " " << N->getFunction().getName() << "\n";
243 PreservedAnalyses LazyCallGraphPrinterPass::run(Module *M,
244 ModuleAnalysisManager *AM) {
245 LazyCallGraph &G = AM->getResult<LazyCallGraphAnalysis>(M);
247 OS << "Printing the call graph for module: " << M->getModuleIdentifier()
250 SmallPtrSet<LazyCallGraph::Node *, 16> Printed;
251 for (LazyCallGraph::Node *N : G)
252 if (Printed.insert(N))
253 printNodes(OS, *N, Printed);
255 for (LazyCallGraph::SCC *SCC : G.postorder_sccs())
258 return PreservedAnalyses::all();