1//===- llvm/Analysis/DDG.h --------------------------------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file defines the Data-Dependence Graph (DDG).
10//
11//===----------------------------------------------------------------------===//
12
13#ifndef LLVM_ANALYSIS_DDG_H
14#define LLVM_ANALYSIS_DDG_H
15
16#include "llvm/ADT/DenseMap.h"
17#include "llvm/ADT/DirectedGraph.h"
18#include "llvm/Analysis/DependenceAnalysis.h"
19#include "llvm/Analysis/DependenceGraphBuilder.h"
20#include "llvm/Analysis/LoopAnalysisManager.h"
21
22namespace llvm {
23class Function;
24class Loop;
25class LoopInfo;
26class DDGNode;
27class DDGEdge;
28using DDGNodeBase = DGNode<DDGNode, DDGEdge>;
29using DDGEdgeBase = DGEdge<DDGNode, DDGEdge>;
30using DDGBase = DirectedGraph<DDGNode, DDGEdge>;
31class LPMUpdater;
32
33/// Data Dependence Graph Node
34/// The graph can represent the following types of nodes:
35/// 1. Single instruction node containing just one instruction.
36/// 2. Multiple instruction node where two or more instructions from
37/// the same basic block are merged into one node.
38/// 3. Pi-block node which is a group of other DDG nodes that are part of a
39/// strongly-connected component of the graph.
40/// A pi-block node contains more than one single or multiple instruction
41/// nodes. The root node cannot be part of a pi-block.
42/// 4. Root node is a special node that connects to all components such that
43/// there is always a path from it to any node in the graph.
44class DDGNode : public DDGNodeBase {
45public:
46 using InstructionListType = SmallVectorImpl<Instruction *>;
47
48 enum class NodeKind {
49 Unknown,
50 SingleInstruction,
51 MultiInstruction,
52 PiBlock,
53 Root,
54 };
55
56 DDGNode() = delete;
57 DDGNode(const NodeKind K) : Kind(K) {}
58 DDGNode(const DDGNode &N) = default;
59 DDGNode(DDGNode &&N) : DDGNodeBase(std::move(N)), Kind(N.Kind) {}
60 virtual ~DDGNode() = 0;
61
62 DDGNode &operator=(const DDGNode &N) {
63 DGNode::operator=(N);
64 Kind = N.Kind;
65 return *this;
66 }
67
68 DDGNode &operator=(DDGNode &&N) {
69 DGNode::operator=(N: std::move(N));
70 Kind = N.Kind;
71 return *this;
72 }
73
74 /// Getter for the kind of this node.
75 NodeKind getKind() const { return Kind; }
76
77 /// Collect a list of instructions, in \p IList, for which predicate \p Pred
78 /// evaluates to true when iterating over instructions of this node. Return
79 /// true if at least one instruction was collected, and false otherwise.
80 bool collectInstructions(llvm::function_ref<bool(Instruction *)> const &Pred,
81 InstructionListType &IList) const;
82
83protected:
84 /// Setter for the kind of this node.
85 void setKind(NodeKind K) { Kind = K; }
86
87private:
88 NodeKind Kind;
89};
90
91/// Subclass of DDGNode representing the root node of the graph.
92/// There should only be one such node in a given graph.
93class RootDDGNode : public DDGNode {
94public:
95 RootDDGNode() : DDGNode(NodeKind::Root) {}
96 RootDDGNode(const RootDDGNode &N) = delete;
97 RootDDGNode(RootDDGNode &&N) : DDGNode(std::move(N)) {}
98 ~RootDDGNode() = default;
99
100 /// Define classof to be able to use isa<>, cast<>, dyn_cast<>, etc.
101 static bool classof(const DDGNode *N) {
102 return N->getKind() == NodeKind::Root;
103 }
104 static bool classof(const RootDDGNode *N) { return true; }
105};
106
107/// Subclass of DDGNode representing single or multi-instruction nodes.
108class SimpleDDGNode : public DDGNode {
109 friend class DDGBuilder;
110
111public:
112 SimpleDDGNode() = delete;
113 SimpleDDGNode(Instruction &I);
114 SimpleDDGNode(const SimpleDDGNode &N);
115 SimpleDDGNode(SimpleDDGNode &&N);
116 ~SimpleDDGNode();
117
118 SimpleDDGNode &operator=(const SimpleDDGNode &N) = default;
119
120 SimpleDDGNode &operator=(SimpleDDGNode &&N) {
121 DDGNode::operator=(N: std::move(N));
122 InstList = std::move(N.InstList);
123 return *this;
124 }
125
126 /// Get the list of instructions in this node.
127 const InstructionListType &getInstructions() const {
128 assert(!InstList.empty() && "Instruction List is empty.");
129 return InstList;
130 }
131 InstructionListType &getInstructions() {
132 return const_cast<InstructionListType &>(
133 static_cast<const SimpleDDGNode *>(this)->getInstructions());
134 }
135
136 /// Get the first/last instruction in the node.
137 Instruction *getFirstInstruction() const { return getInstructions().front(); }
138 Instruction *getLastInstruction() const { return getInstructions().back(); }
139
140 /// Define classof to be able to use isa<>, cast<>, dyn_cast<>, etc.
141 static bool classof(const DDGNode *N) {
142 return N->getKind() == NodeKind::SingleInstruction ||
143 N->getKind() == NodeKind::MultiInstruction;
144 }
145 static bool classof(const SimpleDDGNode *N) { return true; }
146
147private:
148 /// Append the list of instructions in \p Input to this node.
149 void appendInstructions(const InstructionListType &Input) {
150 setKind((InstList.size() == 0 && Input.size() == 1)
151 ? NodeKind::SingleInstruction
152 : NodeKind::MultiInstruction);
153 llvm::append_range(C&: InstList, R: Input);
154 }
155 void appendInstructions(const SimpleDDGNode &Input) {
156 appendInstructions(Input: Input.getInstructions());
157 }
158
159 /// List of instructions associated with a single or multi-instruction node.
160 SmallVector<Instruction *, 2> InstList;
161};
162
163/// Subclass of DDGNode representing a pi-block. A pi-block represents a group
164/// of DDG nodes that are part of a strongly-connected component of the graph.
165/// Replacing all the SCCs with pi-blocks results in an acyclic representation
166/// of the DDG. For example if we have:
167/// {a -> b}, {b -> c, d}, {c -> a}
168/// the cycle a -> b -> c -> a is abstracted into a pi-block "p" as follows:
169/// {p -> d} with "p" containing: {a -> b}, {b -> c}, {c -> a}
170class PiBlockDDGNode : public DDGNode {
171public:
172 using PiNodeList = SmallVector<DDGNode *, 4>;
173
174 PiBlockDDGNode() = delete;
175 PiBlockDDGNode(const PiNodeList &List);
176 PiBlockDDGNode(const PiBlockDDGNode &N);
177 PiBlockDDGNode(PiBlockDDGNode &&N);
178 ~PiBlockDDGNode();
179
180 PiBlockDDGNode &operator=(const PiBlockDDGNode &N) = default;
181
182 PiBlockDDGNode &operator=(PiBlockDDGNode &&N) {
183 DDGNode::operator=(N: std::move(N));
184 NodeList = std::move(N.NodeList);
185 return *this;
186 }
187
188 /// Get the list of nodes in this pi-block.
189 const PiNodeList &getNodes() const {
190 assert(!NodeList.empty() && "Node list is empty.");
191 return NodeList;
192 }
193 PiNodeList &getNodes() {
194 return const_cast<PiNodeList &>(
195 static_cast<const PiBlockDDGNode *>(this)->getNodes());
196 }
197
198 /// Define classof to be able to use isa<>, cast<>, dyn_cast<>, etc.
199 static bool classof(const DDGNode *N) {
200 return N->getKind() == NodeKind::PiBlock;
201 }
202
203private:
204 /// List of nodes in this pi-block.
205 PiNodeList NodeList;
206};
207
208/// Data Dependency Graph Edge.
209/// An edge in the DDG can represent a def-use relationship or
210/// a memory dependence based on the result of DependenceAnalysis.
211/// A rooted edge connects the root node to one of the components
212/// of the graph.
213class DDGEdge : public DDGEdgeBase {
214public:
215 /// The kind of edge in the DDG
216 enum class EdgeKind {
217 Unknown,
218 RegisterDefUse,
219 MemoryDependence,
220 Rooted,
221 Last = Rooted // Must be equal to the largest enum value.
222 };
223
224 explicit DDGEdge(DDGNode &N) = delete;
225 DDGEdge(DDGNode &N, EdgeKind K) : DDGEdgeBase(N), Kind(K) {}
226 DDGEdge(const DDGEdge &E) : DDGEdgeBase(E), Kind(E.getKind()) {}
227 DDGEdge(DDGEdge &&E) : DDGEdgeBase(std::move(E)), Kind(E.Kind) {}
228 DDGEdge &operator=(const DDGEdge &E) = default;
229
230 DDGEdge &operator=(DDGEdge &&E) {
231 DDGEdgeBase::operator=(E: std::move(E));
232 Kind = E.Kind;
233 return *this;
234 }
235
236 /// Get the edge kind
237 EdgeKind getKind() const { return Kind; };
238
239 /// Return true if this is a def-use edge, and false otherwise.
240 bool isDefUse() const { return Kind == EdgeKind::RegisterDefUse; }
241
242 /// Return true if this is a memory dependence edge, and false otherwise.
243 bool isMemoryDependence() const { return Kind == EdgeKind::MemoryDependence; }
244
245 /// Return true if this is an edge stemming from the root node, and false
246 /// otherwise.
247 bool isRooted() const { return Kind == EdgeKind::Rooted; }
248
249private:
250 EdgeKind Kind;
251};
252
253/// Encapsulate some common data and functionality needed for different
254/// variations of data dependence graphs.
255template <typename NodeType> class DependenceGraphInfo {
256public:
257 using DependenceList = SmallVector<std::unique_ptr<Dependence>, 1>;
258
259 DependenceGraphInfo() = delete;
260 DependenceGraphInfo(const DependenceGraphInfo &G) = delete;
261 DependenceGraphInfo(const std::string &N, const DependenceInfo &DepInfo)
262 : Name(N), DI(DepInfo), Root(nullptr) {}
263 DependenceGraphInfo(DependenceGraphInfo &&G)
264 : Name(std::move(G.Name)), DI(std::move(G.DI)), Root(G.Root) {}
265 virtual ~DependenceGraphInfo() = default;
266
267 /// Return the label that is used to name this graph.
268 StringRef getName() const { return Name; }
269
270 /// Return the root node of the graph.
271 NodeType &getRoot() const {
272 assert(Root && "Root node is not available yet. Graph construction may "
273 "still be in progress\n");
274 return *Root;
275 }
276
277 /// Collect all the data dependency infos coming from any pair of memory
278 /// accesses from \p Src to \p Dst, and store them into \p Deps. Return true
279 /// if a dependence exists, and false otherwise.
280 bool getDependencies(const NodeType &Src, const NodeType &Dst,
281 DependenceList &Deps) const;
282
283 /// Return a string representing the type of dependence that the dependence
284 /// analysis identified between the two given nodes. This function assumes
285 /// that there is a memory dependence between the given two nodes.
286 std::string getDependenceString(const NodeType &Src,
287 const NodeType &Dst) const;
288
289protected:
290 // Name of the graph.
291 std::string Name;
292
293 // Store a copy of DependenceInfo in the graph, so that individual memory
294 // dependencies don't need to be stored. Instead when the dependence is
295 // queried it is recomputed using @DI.
296 const DependenceInfo DI;
297
298 // A special node in the graph that has an edge to every connected component of
299 // the graph, to ensure all nodes are reachable in a graph walk.
300 NodeType *Root = nullptr;
301};
302
303using DDGInfo = DependenceGraphInfo<DDGNode>;
304
305/// Data Dependency Graph
306class DataDependenceGraph : public DDGBase, public DDGInfo {
307 friend AbstractDependenceGraphBuilder<DataDependenceGraph>;
308 friend class DDGBuilder;
309
310public:
311 using NodeType = DDGNode;
312 using EdgeType = DDGEdge;
313
314 DataDependenceGraph() = delete;
315 DataDependenceGraph(const DataDependenceGraph &G) = delete;
316 DataDependenceGraph(DataDependenceGraph &&G)
317 : DDGBase(std::move(G)), DDGInfo(std::move(G)) {}
318 DataDependenceGraph(Function &F, DependenceInfo &DI);
319 DataDependenceGraph(Loop &L, LoopInfo &LI, DependenceInfo &DI);
320 ~DataDependenceGraph();
321
322 /// If node \p N belongs to a pi-block return a pointer to the pi-block,
323 /// otherwise return null.
324 const PiBlockDDGNode *getPiBlock(const NodeType &N) const;
325
326protected:
327 /// Add node \p N to the graph, if it's not added yet, and keep track of the
328 /// root node as well as pi-blocks and their members. Return true if node is
329 /// successfully added.
330 bool addNode(NodeType &N);
331
332private:
333 using PiBlockMapType = DenseMap<const NodeType *, const PiBlockDDGNode *>;
334
335 /// Mapping from graph nodes to their containing pi-blocks. If a node is not
336 /// part of a pi-block, it will not appear in this map.
337 PiBlockMapType PiBlockMap;
338};
339
340/// Concrete implementation of a pure data dependence graph builder. This class
341/// provides custom implementation for the pure-virtual functions used in the
342/// generic dependence graph build algorithm.
343///
344/// For information about time complexity of the build algorithm see the
345/// comments near the declaration of AbstractDependenceGraphBuilder.
346class DDGBuilder : public AbstractDependenceGraphBuilder<DataDependenceGraph> {
347public:
348 DDGBuilder(DataDependenceGraph &G, DependenceInfo &D,
349 const BasicBlockListType &BBs)
350 : AbstractDependenceGraphBuilder(G, D, BBs) {}
351 DDGNode &createRootNode() final {
352 auto *RN = new RootDDGNode();
353 assert(RN && "Failed to allocate memory for DDG root node.");
354 Graph.addNode(N&: *RN);
355 return *RN;
356 }
357 DDGNode &createFineGrainedNode(Instruction &I) final {
358 auto *SN = new SimpleDDGNode(I);
359 assert(SN && "Failed to allocate memory for simple DDG node.");
360 Graph.addNode(N&: *SN);
361 return *SN;
362 }
363 DDGNode &createPiBlock(const NodeListType &L) final {
364 auto *Pi = new PiBlockDDGNode(L);
365 assert(Pi && "Failed to allocate memory for pi-block node.");
366 Graph.addNode(N&: *Pi);
367 return *Pi;
368 }
369 DDGEdge &createDefUseEdge(DDGNode &Src, DDGNode &Tgt) final {
370 auto *E = new DDGEdge(Tgt, DDGEdge::EdgeKind::RegisterDefUse);
371 assert(E && "Failed to allocate memory for edge");
372 Graph.connect(Src, Dst&: Tgt, E&: *E);
373 return *E;
374 }
375 DDGEdge &createMemoryEdge(DDGNode &Src, DDGNode &Tgt) final {
376 auto *E = new DDGEdge(Tgt, DDGEdge::EdgeKind::MemoryDependence);
377 assert(E && "Failed to allocate memory for edge");
378 Graph.connect(Src, Dst&: Tgt, E&: *E);
379 return *E;
380 }
381 DDGEdge &createRootedEdge(DDGNode &Src, DDGNode &Tgt) final {
382 auto *E = new DDGEdge(Tgt, DDGEdge::EdgeKind::Rooted);
383 assert(E && "Failed to allocate memory for edge");
384 assert(isa<RootDDGNode>(Src) && "Expected root node");
385 Graph.connect(Src, Dst&: Tgt, E&: *E);
386 return *E;
387 }
388
389 const NodeListType &getNodesInPiBlock(const DDGNode &N) final {
390 auto *PiNode = dyn_cast<const PiBlockDDGNode>(Val: &N);
391 assert(PiNode && "Expected a pi-block node.");
392 return PiNode->getNodes();
393 }
394
395 /// Return true if the two nodes \pSrc and \pTgt are both simple nodes and
396 /// the consecutive instructions after merging belong to the same basic block.
397 bool areNodesMergeable(const DDGNode &Src, const DDGNode &Tgt) const final;
398 void mergeNodes(DDGNode &Src, DDGNode &Tgt) final;
399 bool shouldSimplify() const final;
400 bool shouldCreatePiBlocks() const final;
401};
402
403raw_ostream &operator<<(raw_ostream &OS, const DDGNode &N);
404raw_ostream &operator<<(raw_ostream &OS, const DDGNode::NodeKind K);
405raw_ostream &operator<<(raw_ostream &OS, const DDGEdge &E);
406raw_ostream &operator<<(raw_ostream &OS, const DDGEdge::EdgeKind K);
407raw_ostream &operator<<(raw_ostream &OS, const DataDependenceGraph &G);
408
409//===--------------------------------------------------------------------===//
410// DDG Analysis Passes
411//===--------------------------------------------------------------------===//
412
413/// Analysis pass that builds the DDG for a loop.
414class DDGAnalysis : public AnalysisInfoMixin<DDGAnalysis> {
415public:
416 using Result = std::unique_ptr<DataDependenceGraph>;
417 Result run(Loop &L, LoopAnalysisManager &AM, LoopStandardAnalysisResults &AR);
418
419private:
420 friend AnalysisInfoMixin<DDGAnalysis>;
421 static AnalysisKey Key;
422};
423
424/// Textual printer pass for the DDG of a loop.
425class DDGAnalysisPrinterPass : public PassInfoMixin<DDGAnalysisPrinterPass> {
426public:
427 explicit DDGAnalysisPrinterPass(raw_ostream &OS) : OS(OS) {}
428 PreservedAnalyses run(Loop &L, LoopAnalysisManager &AM,
429 LoopStandardAnalysisResults &AR, LPMUpdater &U);
430 static bool isRequired() { return true; }
431
432private:
433 raw_ostream &OS;
434};
435
436//===--------------------------------------------------------------------===//
437// DependenceGraphInfo Implementation
438//===--------------------------------------------------------------------===//
439
440template <typename NodeType>
441bool DependenceGraphInfo<NodeType>::getDependencies(
442 const NodeType &Src, const NodeType &Dst, DependenceList &Deps) const {
443 assert(Deps.empty() && "Expected empty output list at the start.");
444
445 // List of memory access instructions from src and dst nodes.
446 SmallVector<Instruction *, 8> SrcIList, DstIList;
447 auto isMemoryAccess = [](const Instruction *I) {
448 return I->mayReadOrWriteMemory();
449 };
450 Src.collectInstructions(isMemoryAccess, SrcIList);
451 Dst.collectInstructions(isMemoryAccess, DstIList);
452
453 for (auto *SrcI : SrcIList)
454 for (auto *DstI : DstIList)
455 if (auto Dep =
456 const_cast<DependenceInfo *>(&DI)->depends(Src: SrcI, Dst: DstI, PossiblyLoopIndependent: true))
457 Deps.push_back(Elt: std::move(Dep));
458
459 return !Deps.empty();
460}
461
462template <typename NodeType>
463std::string
464DependenceGraphInfo<NodeType>::getDependenceString(const NodeType &Src,
465 const NodeType &Dst) const {
466 std::string Str;
467 raw_string_ostream OS(Str);
468 DependenceList Deps;
469 if (!getDependencies(Src, Dst, Deps))
470 return OS.str();
471 interleaveComma(Deps, OS, [&](const std::unique_ptr<Dependence> &D) {
472 D->dump(OS);
473 // Remove the extra new-line character printed by the dump
474 // method
475 if (OS.str().back() == '\n')
476 OS.str().pop_back();
477 });
478
479 return OS.str();
480}
481
482//===--------------------------------------------------------------------===//
483// GraphTraits specializations for the DDG
484//===--------------------------------------------------------------------===//
485
486/// non-const versions of the grapth trait specializations for DDG
487template <> struct GraphTraits<DDGNode *> {
488 using NodeRef = DDGNode *;
489
490 static DDGNode *DDGGetTargetNode(DGEdge<DDGNode, DDGEdge> *P) {
491 return &P->getTargetNode();
492 }
493
494 // Provide a mapped iterator so that the GraphTrait-based implementations can
495 // find the target nodes without having to explicitly go through the edges.
496 using ChildIteratorType =
497 mapped_iterator<DDGNode::iterator, decltype(&DDGGetTargetNode)>;
498 using ChildEdgeIteratorType = DDGNode::iterator;
499
500 static NodeRef getEntryNode(NodeRef N) { return N; }
501 static ChildIteratorType child_begin(NodeRef N) {
502 return ChildIteratorType(N->begin(), &DDGGetTargetNode);
503 }
504 static ChildIteratorType child_end(NodeRef N) {
505 return ChildIteratorType(N->end(), &DDGGetTargetNode);
506 }
507
508 static ChildEdgeIteratorType child_edge_begin(NodeRef N) {
509 return N->begin();
510 }
511 static ChildEdgeIteratorType child_edge_end(NodeRef N) { return N->end(); }
512};
513
514template <>
515struct GraphTraits<DataDependenceGraph *> : public GraphTraits<DDGNode *> {
516 using nodes_iterator = DataDependenceGraph::iterator;
517 static NodeRef getEntryNode(DataDependenceGraph *DG) {
518 return &DG->getRoot();
519 }
520 static nodes_iterator nodes_begin(DataDependenceGraph *DG) {
521 return DG->begin();
522 }
523 static nodes_iterator nodes_end(DataDependenceGraph *DG) { return DG->end(); }
524};
525
526/// const versions of the grapth trait specializations for DDG
527template <> struct GraphTraits<const DDGNode *> {
528 using NodeRef = const DDGNode *;
529
530 static const DDGNode *DDGGetTargetNode(const DGEdge<DDGNode, DDGEdge> *P) {
531 return &P->getTargetNode();
532 }
533
534 // Provide a mapped iterator so that the GraphTrait-based implementations can
535 // find the target nodes without having to explicitly go through the edges.
536 using ChildIteratorType =
537 mapped_iterator<DDGNode::const_iterator, decltype(&DDGGetTargetNode)>;
538 using ChildEdgeIteratorType = DDGNode::const_iterator;
539
540 static NodeRef getEntryNode(NodeRef N) { return N; }
541 static ChildIteratorType child_begin(NodeRef N) {
542 return ChildIteratorType(N->begin(), &DDGGetTargetNode);
543 }
544 static ChildIteratorType child_end(NodeRef N) {
545 return ChildIteratorType(N->end(), &DDGGetTargetNode);
546 }
547
548 static ChildEdgeIteratorType child_edge_begin(NodeRef N) {
549 return N->begin();
550 }
551 static ChildEdgeIteratorType child_edge_end(NodeRef N) { return N->end(); }
552};
553
554template <>
555struct GraphTraits<const DataDependenceGraph *>
556 : public GraphTraits<const DDGNode *> {
557 using nodes_iterator = DataDependenceGraph::const_iterator;
558 static NodeRef getEntryNode(const DataDependenceGraph *DG) {
559 return &DG->getRoot();
560 }
561 static nodes_iterator nodes_begin(const DataDependenceGraph *DG) {
562 return DG->begin();
563 }
564 static nodes_iterator nodes_end(const DataDependenceGraph *DG) {
565 return DG->end();
566 }
567};
568
569} // namespace llvm
570
571#endif // LLVM_ANALYSIS_DDG_H
572

source code of llvm/include/llvm/Analysis/DDG.h