1//===- RegAllocPBQP.h -------------------------------------------*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file defines the PBQPBuilder interface, for classes which build PBQP
11// instances to represent register allocation problems, and the RegAllocPBQP
12// interface.
13//
14//===----------------------------------------------------------------------===//
15
16#ifndef LLVM_CODEGEN_REGALLOCPBQP_H
17#define LLVM_CODEGEN_REGALLOCPBQP_H
18
19#include "llvm/ADT/DenseMap.h"
20#include "llvm/ADT/Hashing.h"
21#include "llvm/CodeGen/PBQP/CostAllocator.h"
22#include "llvm/CodeGen/PBQP/Graph.h"
23#include "llvm/CodeGen/PBQP/Math.h"
24#include "llvm/CodeGen/PBQP/ReductionRules.h"
25#include "llvm/CodeGen/PBQP/Solution.h"
26#include "llvm/Support/ErrorHandling.h"
27#include <algorithm>
28#include <cassert>
29#include <cstddef>
30#include <limits>
31#include <memory>
32#include <set>
33#include <vector>
34
35namespace llvm {
36
37class FunctionPass;
38class LiveIntervals;
39class MachineBlockFrequencyInfo;
40class MachineFunction;
41class raw_ostream;
42
43namespace PBQP {
44namespace RegAlloc {
45
46/// @brief Spill option index.
47inline unsigned getSpillOptionIdx() { return 0; }
48
49/// \brief Metadata to speed allocatability test.
50///
51/// Keeps track of the number of infinities in each row and column.
52class MatrixMetadata {
53public:
54  MatrixMetadata(const Matrix& M)
55    : UnsafeRows(new bool[M.getRows() - 1]()),
56      UnsafeCols(new bool[M.getCols() - 1]()) {
57    unsigned* ColCounts = new unsigned[M.getCols() - 1]();
58
59    for (unsigned i = 1; i < M.getRows(); ++i) {
60      unsigned RowCount = 0;
61      for (unsigned j = 1; j < M.getCols(); ++j) {
62        if (M[i][j] == std::numeric_limits<PBQPNum>::infinity()) {
63          ++RowCount;
64          ++ColCounts[j - 1];
65          UnsafeRows[i - 1] = true;
66          UnsafeCols[j - 1] = true;
67        }
68      }
69      WorstRow = std::max(WorstRow, RowCount);
70    }
71    unsigned WorstColCountForCurRow =
72      *std::max_element(ColCounts, ColCounts + M.getCols() - 1);
73    WorstCol = std::max(WorstCol, WorstColCountForCurRow);
74    delete[] ColCounts;
75  }
76
77  MatrixMetadata(const MatrixMetadata &) = delete;
78  MatrixMetadata &operator=(const MatrixMetadata &) = delete;
79
80  unsigned getWorstRow() const { return WorstRow; }
81  unsigned getWorstCol() const { return WorstCol; }
82  const bool* getUnsafeRows() const { return UnsafeRows.get(); }
83  const bool* getUnsafeCols() const { return UnsafeCols.get(); }
84
85private:
86  unsigned WorstRow = 0;
87  unsigned WorstCol = 0;
88  std::unique_ptr<bool[]> UnsafeRows;
89  std::unique_ptr<bool[]> UnsafeCols;
90};
91
92/// \brief Holds a vector of the allowed physical regs for a vreg.
93class AllowedRegVector {
94  friend hash_code hash_value(const AllowedRegVector &);
95
96public:
97  AllowedRegVector() = default;
98  AllowedRegVector(AllowedRegVector &&) = default;
99
100  AllowedRegVector(const std::vector<unsigned> &OptVec)
101    : NumOpts(OptVec.size()), Opts(new unsigned[NumOpts]) {
102    std::copy(OptVec.begin(), OptVec.end(), Opts.get());
103  }
104
105  unsigned size() const { return NumOpts; }
106  unsigned operator[](size_t I) const { return Opts[I]; }
107
108  bool operator==(const AllowedRegVector &Other) const {
109    if (NumOpts != Other.NumOpts)
110      return false;
111    return std::equal(Opts.get(), Opts.get() + NumOpts, Other.Opts.get());
112  }
113
114  bool operator!=(const AllowedRegVector &Other) const {
115    return !(*this == Other);
116  }
117
118private:
119  unsigned NumOpts = 0;
120  std::unique_ptr<unsigned[]> Opts;
121};
122
123inline hash_code hash_value(const AllowedRegVector &OptRegs) {
124  unsigned *OStart = OptRegs.Opts.get();
125  unsigned *OEnd = OptRegs.Opts.get() + OptRegs.NumOpts;
126  return hash_combine(OptRegs.NumOpts,
127                      hash_combine_range(OStart, OEnd));
128}
129
130/// \brief Holds graph-level metadata relevant to PBQP RA problems.
131class GraphMetadata {
132private:
133  using AllowedRegVecPool = ValuePool<AllowedRegVector>;
134
135public:
136  using AllowedRegVecRef = AllowedRegVecPool::PoolRef;
137
138  GraphMetadata(MachineFunction &MF,
139                LiveIntervals &LIS,
140                MachineBlockFrequencyInfo &MBFI)
141    : MF(MF), LIS(LIS), MBFI(MBFI) {}
142
143  MachineFunction &MF;
144  LiveIntervals &LIS;
145  MachineBlockFrequencyInfo &MBFI;
146
147  void setNodeIdForVReg(unsigned VReg, GraphBase::NodeId NId) {
148    VRegToNodeId[VReg] = NId;
149  }
150
151  GraphBase::NodeId getNodeIdForVReg(unsigned VReg) const {
152    auto VRegItr = VRegToNodeId.find(VReg);
153    if (VRegItr == VRegToNodeId.end())
154      return GraphBase::invalidNodeId();
155    return VRegItr->second;
156  }
157
158  AllowedRegVecRef getAllowedRegs(AllowedRegVector Allowed) {
159    return AllowedRegVecs.getValue(std::move(Allowed));
160  }
161
162private:
163  DenseMap<unsigned, GraphBase::NodeId> VRegToNodeId;
164  AllowedRegVecPool AllowedRegVecs;
165};
166
167/// \brief Holds solver state and other metadata relevant to each PBQP RA node.
168class NodeMetadata {
169public:
170  using AllowedRegVector = RegAlloc::AllowedRegVector;
171
172  // The node's reduction state. The order in this enum is important,
173  // as it is assumed nodes can only progress up (i.e. towards being
174  // optimally reducible) when reducing the graph.
175  using ReductionState = enum {
176    Unprocessed,
177    NotProvablyAllocatable,
178    ConservativelyAllocatable,
179    OptimallyReducible
180  };
181
182  NodeMetadata() = default;
183
184  NodeMetadata(const NodeMetadata &Other)
185    : RS(Other.RS), NumOpts(Other.NumOpts), DeniedOpts(Other.DeniedOpts),
186      OptUnsafeEdges(new unsigned[NumOpts]), VReg(Other.VReg),
187      AllowedRegs(Other.AllowedRegs)
188#ifndef NDEBUG
189      , everConservativelyAllocatable(Other.everConservativelyAllocatable)
190#endif
191  {
192    if (NumOpts > 0) {
193      std::copy(&Other.OptUnsafeEdges[0], &Other.OptUnsafeEdges[NumOpts],
194                &OptUnsafeEdges[0]);
195    }
196  }
197
198  NodeMetadata(NodeMetadata &&) = default;
199  NodeMetadata& operator=(NodeMetadata &&) = default;
200
201  void setVReg(unsigned VReg) { this->VReg = VReg; }
202  unsigned getVReg() const { return VReg; }
203
204  void setAllowedRegs(GraphMetadata::AllowedRegVecRef AllowedRegs) {
205    this->AllowedRegs = std::move(AllowedRegs);
206  }
207  const AllowedRegVector& getAllowedRegs() const { return *AllowedRegs; }
208
209  void setup(const Vector& Costs) {
210    NumOpts = Costs.getLength() - 1;
211    OptUnsafeEdges = std::unique_ptr<unsigned[]>(new unsigned[NumOpts]());
212  }
213
214  ReductionState getReductionState() const { return RS; }
215  void setReductionState(ReductionState RS) {
216    assert(RS >= this->RS && "A node's reduction state can not be downgraded");
217    this->RS = RS;
218
219#ifndef NDEBUG
220    // Remember this state to assert later that a non-infinite register
221    // option was available.
222    if (RS == ConservativelyAllocatable)
223      everConservativelyAllocatable = true;
224#endif
225  }
226
227  void handleAddEdge(const MatrixMetadata& MD, bool Transpose) {
228    DeniedOpts += Transpose ? MD.getWorstRow() : MD.getWorstCol();
229    const bool* UnsafeOpts =
230      Transpose ? MD.getUnsafeCols() : MD.getUnsafeRows();
231    for (unsigned i = 0; i < NumOpts; ++i)
232      OptUnsafeEdges[i] += UnsafeOpts[i];
233  }
234
235  void handleRemoveEdge(const MatrixMetadata& MD, bool Transpose) {
236    DeniedOpts -= Transpose ? MD.getWorstRow() : MD.getWorstCol();
237    const bool* UnsafeOpts =
238      Transpose ? MD.getUnsafeCols() : MD.getUnsafeRows();
239    for (unsigned i = 0; i < NumOpts; ++i)
240      OptUnsafeEdges[i] -= UnsafeOpts[i];
241  }
242
243  bool isConservativelyAllocatable() const {
244    return (DeniedOpts < NumOpts) ||
245      (std::find(&OptUnsafeEdges[0], &OptUnsafeEdges[NumOpts], 0) !=
246       &OptUnsafeEdges[NumOpts]);
247  }
248
249#ifndef NDEBUG
250  bool wasConservativelyAllocatable() const {
251    return everConservativelyAllocatable;
252  }
253#endif
254
255private:
256  ReductionState RS = Unprocessed;
257  unsigned NumOpts = 0;
258  unsigned DeniedOpts = 0;
259  std::unique_ptr<unsigned[]> OptUnsafeEdges;
260  unsigned VReg = 0;
261  GraphMetadata::AllowedRegVecRef AllowedRegs;
262
263#ifndef NDEBUG
264  bool everConservativelyAllocatable = false;
265#endif
266};
267
268class RegAllocSolverImpl {
269private:
270  using RAMatrix = MDMatrix<MatrixMetadata>;
271
272public:
273  using RawVector = PBQP::Vector;
274  using RawMatrix = PBQP::Matrix;
275  using Vector = PBQP::Vector;
276  using Matrix = RAMatrix;
277  using CostAllocator = PBQP::PoolCostAllocator<Vector, Matrix>;
278
279  using NodeId = GraphBase::NodeId;
280  using EdgeId = GraphBase::EdgeId;
281
282  using NodeMetadata = RegAlloc::NodeMetadata;
283  struct EdgeMetadata {};
284  using GraphMetadata = RegAlloc::GraphMetadata;
285
286  using Graph = PBQP::Graph<RegAllocSolverImpl>;
287
288  RegAllocSolverImpl(Graph &G) : G(G) {}
289
290  Solution solve() {
291    G.setSolver(*this);
292    Solution S;
293    setup();
294    S = backpropagate(G, reduce());
295    G.unsetSolver();
296    return S;
297  }
298
299  void handleAddNode(NodeId NId) {
300    assert(G.getNodeCosts(NId).getLength() > 1 &&
301           "PBQP Graph should not contain single or zero-option nodes");
302    G.getNodeMetadata(NId).setup(G.getNodeCosts(NId));
303  }
304
305  void handleRemoveNode(NodeId NId) {}
306  void handleSetNodeCosts(NodeId NId, const Vector& newCosts) {}
307
308  void handleAddEdge(EdgeId EId) {
309    handleReconnectEdge(EId, G.getEdgeNode1Id(EId));
310    handleReconnectEdge(EId, G.getEdgeNode2Id(EId));
311  }
312
313  void handleDisconnectEdge(EdgeId EId, NodeId NId) {
314    NodeMetadata& NMd = G.getNodeMetadata(NId);
315    const MatrixMetadata& MMd = G.getEdgeCosts(EId).getMetadata();
316    NMd.handleRemoveEdge(MMd, NId == G.getEdgeNode2Id(EId));
317    promote(NId, NMd);
318  }
319
320  void handleReconnectEdge(EdgeId EId, NodeId NId) {
321    NodeMetadata& NMd = G.getNodeMetadata(NId);
322    const MatrixMetadata& MMd = G.getEdgeCosts(EId).getMetadata();
323    NMd.handleAddEdge(MMd, NId == G.getEdgeNode2Id(EId));
324  }
325
326  void handleUpdateCosts(EdgeId EId, const Matrix& NewCosts) {
327    NodeId N1Id = G.getEdgeNode1Id(EId);
328    NodeId N2Id = G.getEdgeNode2Id(EId);
329    NodeMetadata& N1Md = G.getNodeMetadata(N1Id);
330    NodeMetadata& N2Md = G.getNodeMetadata(N2Id);
331    bool Transpose = N1Id != G.getEdgeNode1Id(EId);
332
333    // Metadata are computed incrementally. First, update them
334    // by removing the old cost.
335    const MatrixMetadata& OldMMd = G.getEdgeCosts(EId).getMetadata();
336    N1Md.handleRemoveEdge(OldMMd, Transpose);
337    N2Md.handleRemoveEdge(OldMMd, !Transpose);
338
339    // And update now the metadata with the new cost.
340    const MatrixMetadata& MMd = NewCosts.getMetadata();
341    N1Md.handleAddEdge(MMd, Transpose);
342    N2Md.handleAddEdge(MMd, !Transpose);
343
344    // As the metadata may have changed with the update, the nodes may have
345    // become ConservativelyAllocatable or OptimallyReducible.
346    promote(N1Id, N1Md);
347    promote(N2Id, N2Md);
348  }
349
350private:
351  void promote(NodeId NId, NodeMetadata& NMd) {
352    if (G.getNodeDegree(NId) == 3) {
353      // This node is becoming optimally reducible.
354      moveToOptimallyReducibleNodes(NId);
355    } else if (NMd.getReductionState() ==
356               NodeMetadata::NotProvablyAllocatable &&
357               NMd.isConservativelyAllocatable()) {
358      // This node just became conservatively allocatable.
359      moveToConservativelyAllocatableNodes(NId);
360    }
361  }
362
363  void removeFromCurrentSet(NodeId NId) {
364    switch (G.getNodeMetadata(NId).getReductionState()) {
365    case NodeMetadata::Unprocessed: break;
366    case NodeMetadata::OptimallyReducible:
367      assert(OptimallyReducibleNodes.find(NId) !=
368             OptimallyReducibleNodes.end() &&
369             "Node not in optimally reducible set.");
370      OptimallyReducibleNodes.erase(NId);
371      break;
372    case NodeMetadata::ConservativelyAllocatable:
373      assert(ConservativelyAllocatableNodes.find(NId) !=
374             ConservativelyAllocatableNodes.end() &&
375             "Node not in conservatively allocatable set.");
376      ConservativelyAllocatableNodes.erase(NId);
377      break;
378    case NodeMetadata::NotProvablyAllocatable:
379      assert(NotProvablyAllocatableNodes.find(NId) !=
380             NotProvablyAllocatableNodes.end() &&
381             "Node not in not-provably-allocatable set.");
382      NotProvablyAllocatableNodes.erase(NId);
383      break;
384    }
385  }
386
387  void moveToOptimallyReducibleNodes(NodeId NId) {
388    removeFromCurrentSet(NId);
389    OptimallyReducibleNodes.insert(NId);
390    G.getNodeMetadata(NId).setReductionState(
391      NodeMetadata::OptimallyReducible);
392  }
393
394  void moveToConservativelyAllocatableNodes(NodeId NId) {
395    removeFromCurrentSet(NId);
396    ConservativelyAllocatableNodes.insert(NId);
397    G.getNodeMetadata(NId).setReductionState(
398      NodeMetadata::ConservativelyAllocatable);
399  }
400
401  void moveToNotProvablyAllocatableNodes(NodeId NId) {
402    removeFromCurrentSet(NId);
403    NotProvablyAllocatableNodes.insert(NId);
404    G.getNodeMetadata(NId).setReductionState(
405      NodeMetadata::NotProvablyAllocatable);
406  }
407
408  void setup() {
409    // Set up worklists.
410    for (auto NId : G.nodeIds()) {
411      if (G.getNodeDegree(NId) < 3)
412        moveToOptimallyReducibleNodes(NId);
413      else if (G.getNodeMetadata(NId).isConservativelyAllocatable())
414        moveToConservativelyAllocatableNodes(NId);
415      else
416        moveToNotProvablyAllocatableNodes(NId);
417    }
418  }
419
420  // Compute a reduction order for the graph by iteratively applying PBQP
421  // reduction rules. Locally optimal rules are applied whenever possible (R0,
422  // R1, R2). If no locally-optimal rules apply then any conservatively
423  // allocatable node is reduced. Finally, if no conservatively allocatable
424  // node exists then the node with the lowest spill-cost:degree ratio is
425  // selected.
426  std::vector<GraphBase::NodeId> reduce() {
427    assert(!G.empty() && "Cannot reduce empty graph.");
428
429    using NodeId = GraphBase::NodeId;
430    std::vector<NodeId> NodeStack;
431
432    // Consume worklists.
433    while (true) {
434      if (!OptimallyReducibleNodes.empty()) {
435        NodeSet::iterator NItr = OptimallyReducibleNodes.begin();
436        NodeId NId = *NItr;
437        OptimallyReducibleNodes.erase(NItr);
438        NodeStack.push_back(NId);
439        switch (G.getNodeDegree(NId)) {
440        case 0:
441          break;
442        case 1:
443          applyR1(G, NId);
444          break;
445        case 2:
446          applyR2(G, NId);
447          break;
448        default: llvm_unreachable("Not an optimally reducible node.");
449        }
450      } else if (!ConservativelyAllocatableNodes.empty()) {
451        // Conservatively allocatable nodes will never spill. For now just
452        // take the first node in the set and push it on the stack. When we
453        // start optimizing more heavily for register preferencing, it may
454        // would be better to push nodes with lower 'expected' or worst-case
455        // register costs first (since early nodes are the most
456        // constrained).
457        NodeSet::iterator NItr = ConservativelyAllocatableNodes.begin();
458        NodeId NId = *NItr;
459        ConservativelyAllocatableNodes.erase(NItr);
460        NodeStack.push_back(NId);
461        G.disconnectAllNeighborsFromNode(NId);
462      } else if (!NotProvablyAllocatableNodes.empty()) {
463        NodeSet::iterator NItr =
464          std::min_element(NotProvablyAllocatableNodes.begin(),
465                           NotProvablyAllocatableNodes.end(),
466                           SpillCostComparator(G));
467        NodeId NId = *NItr;
468        NotProvablyAllocatableNodes.erase(NItr);
469        NodeStack.push_back(NId);
470        G.disconnectAllNeighborsFromNode(NId);
471      } else
472        break;
473    }
474
475    return NodeStack;
476  }
477
478  class SpillCostComparator {
479  public:
480    SpillCostComparator(const Graph& G) : G(G) {}
481
482    bool operator()(NodeId N1Id, NodeId N2Id) {
483      PBQPNum N1SC = G.getNodeCosts(N1Id)[0];
484      PBQPNum N2SC = G.getNodeCosts(N2Id)[0];
485      if (N1SC == N2SC)
486        return G.getNodeDegree(N1Id) < G.getNodeDegree(N2Id);
487      return N1SC < N2SC;
488    }
489
490  private:
491    const Graph& G;
492  };
493
494  Graph& G;
495  using NodeSet = std::set<NodeId>;
496  NodeSet OptimallyReducibleNodes;
497  NodeSet ConservativelyAllocatableNodes;
498  NodeSet NotProvablyAllocatableNodes;
499};
500
501class PBQPRAGraph : public PBQP::Graph<RegAllocSolverImpl> {
502private:
503  using BaseT = PBQP::Graph<RegAllocSolverImpl>;
504
505public:
506  PBQPRAGraph(GraphMetadata Metadata) : BaseT(std::move(Metadata)) {}
507
508  /// @brief Dump this graph to dbgs().
509  void dump() const;
510
511  /// @brief Dump this graph to an output stream.
512  /// @param OS Output stream to print on.
513  void dump(raw_ostream &OS) const;
514
515  /// @brief Print a representation of this graph in DOT format.
516  /// @param OS Output stream to print on.
517  void printDot(raw_ostream &OS) const;
518};
519
520inline Solution solve(PBQPRAGraph& G) {
521  if (G.empty())
522    return Solution();
523  RegAllocSolverImpl RegAllocSolver(G);
524  return RegAllocSolver.solve();
525}
526
527} // end namespace RegAlloc
528} // end namespace PBQP
529
530/// @brief Create a PBQP register allocator instance.
531FunctionPass *
532createPBQPRegisterAllocator(char *customPassID = nullptr);
533
534} // end namespace llvm
535
536#endif // LLVM_CODEGEN_REGALLOCPBQP_H
537