1 //===- LazyCallGraph.h - Analysis of a Module's call graph ------*- C++ -*-===//
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 //===----------------------------------------------------------------------===//
11 /// Implements a lazy call graph analysis and related passes for the new pass
14 /// NB: This is *not* a traditional call graph! It is a graph which models both
15 /// the current calls and potential calls. As a consequence there are many
16 /// edges in this call graph that do not correspond to a 'call' or 'invoke'
19 /// The primary use cases of this graph analysis is to facilitate iterating
20 /// across the functions of a module in ways that ensure all callees are
21 /// visited prior to a caller (given any SCC constraints), or vice versa. As
22 /// such is it particularly well suited to organizing CGSCC optimizations such
23 /// as inlining, outlining, argument promotion, etc. That is its primary use
24 /// case and motivates the design. It may not be appropriate for other
25 /// purposes. The use graph of functions or some other conservative analysis of
26 /// call instructions may be interesting for optimizations and subsequent
27 /// analyses which don't work in the context of an overly specified
28 /// potential-call-edge graph.
30 /// To understand the specific rules and nature of this call graph analysis,
31 /// see the documentation of the \c LazyCallGraph below.
33 //===----------------------------------------------------------------------===//
35 #ifndef LLVM_ANALYSIS_LAZY_CALL_GRAPH
36 #define LLVM_ANALYSIS_LAZY_CALL_GRAPH
38 #include "llvm/ADT/DenseMap.h"
39 #include "llvm/ADT/PointerUnion.h"
40 #include "llvm/ADT/STLExtras.h"
41 #include "llvm/ADT/SetVector.h"
42 #include "llvm/ADT/SmallPtrSet.h"
43 #include "llvm/ADT/SmallVector.h"
44 #include "llvm/ADT/iterator.h"
45 #include "llvm/ADT/iterator_range.h"
46 #include "llvm/IR/BasicBlock.h"
47 #include "llvm/IR/Function.h"
48 #include "llvm/IR/Module.h"
49 #include "llvm/Support/Allocator.h"
53 class ModuleAnalysisManager;
54 class PreservedAnalyses;
57 /// \brief A lazily constructed view of the call graph of a module.
59 /// With the edges of this graph, the motivating constraint that we are
60 /// attempting to maintain is that function-local optimization, CGSCC-local
61 /// optimizations, and optimizations transforming a pair of functions connected
62 /// by an edge in the graph, do not invalidate a bottom-up traversal of the SCC
63 /// DAG. That is, no optimizations will delete, remove, or add an edge such
64 /// that functions already visited in a bottom-up order of the SCC DAG are no
65 /// longer valid to have visited, or such that functions not yet visited in
66 /// a bottom-up order of the SCC DAG are not required to have already been
69 /// Within this constraint, the desire is to minimize the merge points of the
70 /// SCC DAG. The greater the fanout of the SCC DAG and the fewer merge points
71 /// in the SCC DAG, the more independence there is in optimizing within it.
72 /// There is a strong desire to enable parallelization of optimizations over
73 /// the call graph, and both limited fanout and merge points will (artificially
74 /// in some cases) limit the scaling of such an effort.
76 /// To this end, graph represents both direct and any potential resolution to
77 /// an indirect call edge. Another way to think about it is that it represents
78 /// both the direct call edges and any direct call edges that might be formed
79 /// through static optimizations. Specifically, it considers taking the address
80 /// of a function to be an edge in the call graph because this might be
81 /// forwarded to become a direct call by some subsequent function-local
82 /// optimization. The result is that the graph closely follows the use-def
83 /// edges for functions. Walking "up" the graph can be done by looking at all
84 /// of the uses of a function.
86 /// The roots of the call graph are the external functions and functions
87 /// escaped into global variables. Those functions can be called from outside
88 /// of the module or via unknowable means in the IR -- we may not be able to
89 /// form even a potential call edge from a function body which may dynamically
90 /// load the function and call it.
92 /// This analysis still requires updates to remain valid after optimizations
93 /// which could potentially change the set of potential callees. The
94 /// constraints it operates under only make the traversal order remain valid.
96 /// The entire analysis must be re-computed if full interprocedural
97 /// optimizations run at any point. For example, globalopt completely
98 /// invalidates the information in this analysis.
100 /// FIXME: This class is named LazyCallGraph in a lame attempt to distinguish
101 /// it from the existing CallGraph. At some point, it is expected that this
102 /// will be the only call graph and it will be renamed accordingly.
103 class LazyCallGraph {
107 typedef SmallVector<PointerUnion<Function *, Node *>, 4> NodeVectorT;
108 typedef SmallVectorImpl<PointerUnion<Function *, Node *>> NodeVectorImplT;
110 /// \brief A lazy iterator used for both the entry nodes and child nodes.
112 /// When this iterator is dereferenced, if not yet available, a function will
113 /// be scanned for "calls" or uses of functions and its child information
114 /// will be constructed. All of these results are accumulated and cached in
116 class iterator : public std::iterator<std::bidirectional_iterator_tag, Node> {
117 friend class LazyCallGraph;
118 friend class LazyCallGraph::Node;
120 /// \brief Nonce type to select the constructor for the end iterator.
124 NodeVectorImplT::iterator NI;
126 // Build the begin iterator for a node.
127 explicit iterator(LazyCallGraph &G, NodeVectorImplT &Nodes)
128 : G(&G), NI(Nodes.begin()) {}
130 // Build the end iterator for a node. This is selected purely by overload.
131 iterator(LazyCallGraph &G, NodeVectorImplT &Nodes, IsAtEndT /*Nonce*/)
132 : G(&G), NI(Nodes.end()) {}
135 bool operator==(const iterator &Arg) const { return NI == Arg.NI; }
136 bool operator!=(const iterator &Arg) const { return !operator==(Arg); }
138 reference operator*() const {
139 if (NI->is<Node *>())
140 return *NI->get<Node *>();
142 Function *F = NI->get<Function *>();
143 Node &ChildN = G->get(*F);
147 pointer operator->() const { return &operator*(); }
149 iterator &operator++() {
153 iterator operator++(int) {
154 iterator prev = *this;
159 iterator &operator--() {
163 iterator operator--(int) {
164 iterator next = *this;
170 /// \brief A node in the call graph.
172 /// This represents a single node. It's primary roles are to cache the list of
173 /// callees, de-duplicate and provide fast testing of whether a function is
174 /// a callee, and facilitate iteration of child nodes in the graph.
176 friend class LazyCallGraph;
177 friend class LazyCallGraph::SCC;
182 // We provide for the DFS numbering and Tarjan walk lowlink numbers to be
183 // stored directly within the node.
187 mutable NodeVectorT Callees;
188 DenseMap<Function *, size_t> CalleeIndexMap;
190 /// \brief Basic constructor implements the scanning of F into Callees and
192 Node(LazyCallGraph &G, Function &F);
195 typedef LazyCallGraph::iterator iterator;
197 Function &getFunction() const {
201 iterator begin() const { return iterator(*G, Callees); }
202 iterator end() const { return iterator(*G, Callees, iterator::IsAtEndT()); }
204 /// Equality is defined as address equality.
205 bool operator==(const Node &N) const { return this == &N; }
206 bool operator!=(const Node &N) const { return !operator==(N); }
209 /// \brief An SCC of the call graph.
211 /// This represents a Strongly Connected Component of the call graph as
212 /// a collection of call graph nodes. While the order of nodes in the SCC is
213 /// stable, it is not any particular order.
215 friend class LazyCallGraph;
216 friend class LazyCallGraph::Node;
218 SmallPtrSet<SCC *, 1> ParentSCCs;
219 SmallVector<Node *, 1> Nodes;
223 void insert(LazyCallGraph &G, Node &N);
225 void removeEdge(LazyCallGraph &G, Function &Caller, Function &Callee,
228 SmallVector<LazyCallGraph::SCC *, 1>
229 removeInternalEdge(LazyCallGraph &G, Node &Caller, Node &Callee);
232 typedef SmallVectorImpl<Node *>::const_iterator iterator;
233 typedef pointee_iterator<SmallPtrSet<SCC *, 1>::const_iterator> parent_iterator;
235 iterator begin() const { return Nodes.begin(); }
236 iterator end() const { return Nodes.end(); }
238 parent_iterator parent_begin() const { return ParentSCCs.begin(); }
239 parent_iterator parent_end() const { return ParentSCCs.end(); }
241 iterator_range<parent_iterator> parents() const {
242 return iterator_range<parent_iterator>(parent_begin(), parent_end());
246 /// \brief A post-order depth-first SCC iterator over the call graph.
248 /// This iterator triggers the Tarjan DFS-based formation of the SCC DAG for
249 /// the call graph, walking it lazily in depth-first post-order. That is, it
250 /// always visits SCCs for a callee prior to visiting the SCC for a caller
251 /// (when they are in different SCCs).
252 class postorder_scc_iterator
253 : public std::iterator<std::forward_iterator_tag, SCC> {
254 friend class LazyCallGraph;
255 friend class LazyCallGraph::Node;
257 /// \brief Nonce type to select the constructor for the end iterator.
263 // Build the begin iterator for a node.
264 postorder_scc_iterator(LazyCallGraph &G) : G(&G) {
265 C = G.getNextSCCInPostOrder();
268 // Build the end iterator for a node. This is selected purely by overload.
269 postorder_scc_iterator(LazyCallGraph &G, IsAtEndT /*Nonce*/)
270 : G(&G), C(nullptr) {}
273 bool operator==(const postorder_scc_iterator &Arg) const {
274 return G == Arg.G && C == Arg.C;
276 bool operator!=(const postorder_scc_iterator &Arg) const {
277 return !operator==(Arg);
280 reference operator*() const { return *C; }
281 pointer operator->() const { return &operator*(); }
283 postorder_scc_iterator &operator++() {
284 C = G->getNextSCCInPostOrder();
287 postorder_scc_iterator operator++(int) {
288 postorder_scc_iterator prev = *this;
294 /// \brief Construct a graph for the given module.
296 /// This sets up the graph and computes all of the entry points of the graph.
297 /// No function definitions are scanned until their nodes in the graph are
298 /// requested during traversal.
299 LazyCallGraph(Module &M);
301 LazyCallGraph(LazyCallGraph &&G);
302 LazyCallGraph &operator=(LazyCallGraph &&RHS);
304 iterator begin() { return iterator(*this, EntryNodes); }
305 iterator end() { return iterator(*this, EntryNodes, iterator::IsAtEndT()); }
307 postorder_scc_iterator postorder_scc_begin() {
308 return postorder_scc_iterator(*this);
310 postorder_scc_iterator postorder_scc_end() {
311 return postorder_scc_iterator(*this, postorder_scc_iterator::IsAtEndT());
314 iterator_range<postorder_scc_iterator> postorder_sccs() {
315 return iterator_range<postorder_scc_iterator>(postorder_scc_begin(),
316 postorder_scc_end());
319 /// \brief Lookup a function in the graph which has already been scanned and
321 Node *lookup(const Function &F) const { return NodeMap.lookup(&F); }
323 /// \brief Lookup a function's SCC in the graph.
325 /// \returns null if the function hasn't been assigned an SCC via the SCC
327 SCC *lookupSCC(Node &N) const { return SCCMap.lookup(&N); }
329 /// \brief Get a graph node for a given function, scanning it to populate the
330 /// graph data as necessary.
331 Node &get(Function &F) {
332 Node *&N = NodeMap[&F];
336 return insertInto(F, N);
339 /// \brief Update the call graph after deleting an edge.
340 void removeEdge(Node &Caller, Function &Callee);
342 /// \brief Update the call graph after deleting an edge.
343 void removeEdge(Function &Caller, Function &Callee) {
344 return removeEdge(get(Caller), Callee);
348 /// \brief Allocator that holds all the call graph nodes.
349 SpecificBumpPtrAllocator<Node> BPA;
351 /// \brief Maps function->node for fast lookup.
352 DenseMap<const Function *, Node *> NodeMap;
354 /// \brief The entry nodes to the graph.
356 /// These nodes are reachable through "external" means. Put another way, they
357 /// escape at the module scope.
358 NodeVectorT EntryNodes;
360 /// \brief Map of the entry nodes in the graph to their indices in
362 DenseMap<Function *, size_t> EntryIndexMap;
364 /// \brief Allocator that holds all the call graph SCCs.
365 SpecificBumpPtrAllocator<SCC> SCCBPA;
367 /// \brief Maps Function -> SCC for fast lookup.
368 DenseMap<Node *, SCC *> SCCMap;
370 /// \brief The leaf SCCs of the graph.
372 /// These are all of the SCCs which have no children.
373 SmallVector<SCC *, 4> LeafSCCs;
375 /// \brief Stack of nodes in the DFS walk.
376 SmallVector<std::pair<Node *, iterator>, 4> DFSStack;
378 /// \brief Set of entry nodes not-yet-processed into SCCs.
379 SmallSetVector<Function *, 4> SCCEntryNodes;
381 /// \brief Stack of nodes the DFS has walked but not yet put into a SCC.
382 SmallVector<Node *, 4> PendingSCCStack;
384 /// \brief Counter for the next DFS number to assign.
387 /// \brief Helper to insert a new function, with an already looked-up entry in
389 Node &insertInto(Function &F, Node *&MappedN);
391 /// \brief Helper to update pointers back to the graph object during moves.
392 void updateGraphPtrs();
394 /// \brief Helper to form a new SCC out of the top of a DFSStack-like
396 SCC *formSCC(Node *RootN, SmallVectorImpl<Node *> &NodeStack);
398 /// \brief Retrieve the next node in the post-order SCC walk of the call graph.
399 SCC *getNextSCCInPostOrder();
402 // Provide GraphTraits specializations for call graphs.
403 template <> struct GraphTraits<LazyCallGraph::Node *> {
404 typedef LazyCallGraph::Node NodeType;
405 typedef LazyCallGraph::iterator ChildIteratorType;
407 static NodeType *getEntryNode(NodeType *N) { return N; }
408 static ChildIteratorType child_begin(NodeType *N) { return N->begin(); }
409 static ChildIteratorType child_end(NodeType *N) { return N->end(); }
411 template <> struct GraphTraits<LazyCallGraph *> {
412 typedef LazyCallGraph::Node NodeType;
413 typedef LazyCallGraph::iterator ChildIteratorType;
415 static NodeType *getEntryNode(NodeType *N) { return N; }
416 static ChildIteratorType child_begin(NodeType *N) { return N->begin(); }
417 static ChildIteratorType child_end(NodeType *N) { return N->end(); }
420 /// \brief An analysis pass which computes the call graph for a module.
421 class LazyCallGraphAnalysis {
423 /// \brief Inform generic clients of the result type.
424 typedef LazyCallGraph Result;
426 static void *ID() { return (void *)&PassID; }
428 /// \brief Compute the \c LazyCallGraph for a the module \c M.
430 /// This just builds the set of entry points to the call graph. The rest is
431 /// built lazily as it is walked.
432 LazyCallGraph run(Module *M) { return LazyCallGraph(*M); }
438 /// \brief A pass which prints the call graph to a \c raw_ostream.
440 /// This is primarily useful for testing the analysis.
441 class LazyCallGraphPrinterPass {
445 explicit LazyCallGraphPrinterPass(raw_ostream &OS);
447 PreservedAnalyses run(Module *M, ModuleAnalysisManager *AM);
449 static StringRef name() { return "LazyCallGraphPrinterPass"; }