include/llvm/CodeGen/RegAllocPBQP.h

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