include/llvm/CodeGen/PBQP/RegAllocSolver.h

   1 //===-- RegAllocSolver.h - Heuristic PBQP Solver for reg alloc --*- 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 // Heuristic PBQP solver for register allocation problems. This solver uses a
  11 // graph reduction approach. Nodes of degree 0, 1 and 2 are eliminated with
  12 // optimality-preserving rules (see ReductionRules.h). When no low-degree (<3)
  13 // nodes are present, a heuristic derived from Brigg's graph coloring approach
  14 // is used.
  15 //
  16 //===----------------------------------------------------------------------===//
  17
  18 #ifndef LLVM_CODEGEN_PBQP_REGALLOCSOLVER_H
  19 #define LLVM_CODEGEN_PBQP_REGALLOCSOLVER_H
  20
  21 #include "CostAllocator.h"
  22 #include "Graph.h"
  23 #include "ReductionRules.h"
  24 #include "Solution.h"
  25 #include "llvm/Support/ErrorHandling.h"
  26 #include <limits>
  27 #include <vector>
  28
  29 namespace llvm{
  30 namespace PBQP {
  31   namespace RegAlloc {
  32
  33     /// @brief Spill option index.
  34     inline unsigned getSpillOptionIdx() { return 0; }
  35
  36     /// \brief Metadata to speed allocatability test.
  37     ///
  38     /// Keeps track of the number of infinities in each row and column.
  39     class MatrixMetadata {
  40     private:
  41       MatrixMetadata(const MatrixMetadata&);
  42       void operator=(const MatrixMetadata&);
  43     public:
  44       MatrixMetadata(const PBQP::Matrix& M)
  45         : WorstRow(0), WorstCol(0),
  46           UnsafeRows(new bool[M.getRows() - 1]()),
  47           UnsafeCols(new bool[M.getCols() - 1]()) {
  48
  49         unsigned* ColCounts = new unsigned[M.getCols() - 1]();
  50
  51         for (unsigned i = 1; i < M.getRows(); ++i) {
  52           unsigned RowCount = 0;
  53           for (unsigned j = 1; j < M.getCols(); ++j) {
  54             if (M[i][j] == std::numeric_limits<PBQP::PBQPNum>::infinity()) {
  55               ++RowCount;
  56               ++ColCounts[j - 1];
  57               UnsafeRows[i - 1] = true;
  58               UnsafeCols[j - 1] = true;
  59             }
  60           }
  61           WorstRow = std::max(WorstRow, RowCount);
  62         }
  63         unsigned WorstColCountForCurRow =
  64           *std::max_element(ColCounts, ColCounts + M.getCols() - 1);
  65         WorstCol = std::max(WorstCol, WorstColCountForCurRow);
  66         delete[] ColCounts;
  67       }
  68
  69       ~MatrixMetadata() {
  70         delete[] UnsafeRows;
  71         delete[] UnsafeCols;
  72       }
  73
  74       unsigned getWorstRow() const { return WorstRow; }
  75       unsigned getWorstCol() const { return WorstCol; }
  76       const bool* getUnsafeRows() const { return UnsafeRows; }
  77       const bool* getUnsafeCols() const { return UnsafeCols; }
  78
  79     private:
  80       unsigned WorstRow, WorstCol;
  81       bool* UnsafeRows;
  82       bool* UnsafeCols;
  83     };
  84
  85     class NodeMetadata {
  86     public:
  87       typedef std::vector<unsigned> OptionToRegMap;
  88
  89       typedef enum { Unprocessed,
  90                      OptimallyReducible,
  91                      ConservativelyAllocatable,
  92                      NotProvablyAllocatable } ReductionState;
  93
  94       NodeMetadata() : RS(Unprocessed), DeniedOpts(0), OptUnsafeEdges(nullptr){}
  95       ~NodeMetadata() { delete[] OptUnsafeEdges; }
  96
  97       void setVReg(unsigned VReg) { this->VReg = VReg; }
  98       unsigned getVReg() const { return VReg; }
  99
 100       void setOptionRegs(OptionToRegMap OptionRegs) {
 101         this->OptionRegs = std::move(OptionRegs);
 102       }
 103       const OptionToRegMap& getOptionRegs() const { return OptionRegs; }
 104
 105       void setup(const Vector& Costs) {
 106         NumOpts = Costs.getLength() - 1;
 107         OptUnsafeEdges = new unsigned[NumOpts]();
 108       }
 109
 110       ReductionState getReductionState() const { return RS; }
 111       void setReductionState(ReductionState RS) { this->RS = RS; }
 112
 113       void handleAddEdge(const MatrixMetadata& MD, bool Transpose) {
 114         DeniedOpts += Transpose ? MD.getWorstCol() : MD.getWorstRow();
 115         const bool* UnsafeOpts =
 116           Transpose ? MD.getUnsafeCols() : MD.getUnsafeRows();
 117         for (unsigned i = 0; i < NumOpts; ++i)
 118           OptUnsafeEdges[i] += UnsafeOpts[i];
 119       }
 120
 121       void handleRemoveEdge(const MatrixMetadata& MD, bool Transpose) {
 122         DeniedOpts -= Transpose ? MD.getWorstCol() : MD.getWorstRow();
 123         const bool* UnsafeOpts =
 124           Transpose ? MD.getUnsafeCols() : MD.getUnsafeRows();
 125         for (unsigned i = 0; i < NumOpts; ++i)
 126           OptUnsafeEdges[i] -= UnsafeOpts[i];
 127       }
 128
 129       bool isConservativelyAllocatable() const {
 130         return (DeniedOpts < NumOpts) ||
 131                (std::find(OptUnsafeEdges, OptUnsafeEdges + NumOpts, 0) !=
 132                   OptUnsafeEdges + NumOpts);
 133       }
 134
 135     private:
 136       ReductionState RS;
 137       unsigned NumOpts;
 138       unsigned DeniedOpts;
 139       unsigned* OptUnsafeEdges;
 140       unsigned VReg;
 141       OptionToRegMap OptionRegs;
 142     };
 143
 144     class RegAllocSolverImpl {
 145     private:
 146       typedef PBQP::MDMatrix<MatrixMetadata> RAMatrix;
 147     public:
 148       typedef PBQP::Vector RawVector;
 149       typedef PBQP::Matrix RawMatrix;
 150       typedef PBQP::Vector Vector;
 151       typedef RAMatrix     Matrix;
 152       typedef PBQP::PoolCostAllocator<
 153                 Vector, PBQP::VectorComparator,
 154                 Matrix, PBQP::MatrixComparator> CostAllocator;
 155
 156       typedef PBQP::GraphBase::NodeId NodeId;
 157       typedef PBQP::GraphBase::EdgeId EdgeId;
 158
 159       typedef RegAlloc::NodeMetadata NodeMetadata;
 160
 161       struct EdgeMetadata { };
 162
 163       class GraphMetadata {
 164       public:
 165         GraphMetadata(MachineFunction &MF,
 166                       LiveIntervals &LIS,
 167                       MachineBlockFrequencyInfo &MBFI)
 168           : MF(MF), LIS(LIS), MBFI(MBFI) {}
 169
 170         MachineFunction &MF;
 171         LiveIntervals &LIS;
 172         MachineBlockFrequencyInfo &MBFI;
 173
 174         void setNodeIdForVReg(unsigned VReg, GraphBase::NodeId NId) {
 175           VRegToNodeId[VReg] = NId;
 176         }
 177
 178         GraphBase::NodeId getNodeIdForVReg(unsigned VReg) const {
 179           auto VRegItr = VRegToNodeId.find(VReg);
 180           if (VRegItr == VRegToNodeId.end())
 181             return GraphBase::invalidNodeId();
 182           return VRegItr->second;
 183         }
 184
 185         void eraseNodeIdForVReg(unsigned VReg) {
 186           VRegToNodeId.erase(VReg);
 187         }
 188
 189       private:
 190         DenseMap<unsigned, NodeId> VRegToNodeId;
 191       };
 192
 193       typedef PBQP::Graph<RegAllocSolverImpl> Graph;
 194
 195       RegAllocSolverImpl(Graph &G) : G(G) {}
 196
 197       Solution solve() {
 198         G.setSolver(*this);
 199         Solution S;
 200         setup();
 201         S = backpropagate(G, reduce());
 202         G.unsetSolver();
 203         return S;
 204       }
 205
 206       void handleAddNode(NodeId NId) {
 207         G.getNodeMetadata(NId).setup(G.getNodeCosts(NId));
 208       }
 209       void handleRemoveNode(NodeId NId) {}
 210       void handleSetNodeCosts(NodeId NId, const Vector& newCosts) {}
 211
 212       void handleAddEdge(EdgeId EId) {
 213         handleReconnectEdge(EId, G.getEdgeNode1Id(EId));
 214         handleReconnectEdge(EId, G.getEdgeNode2Id(EId));
 215       }
 216
 217       void handleRemoveEdge(EdgeId EId) {
 218         handleDisconnectEdge(EId, G.getEdgeNode1Id(EId));
 219         handleDisconnectEdge(EId, G.getEdgeNode2Id(EId));
 220       }
 221
 222       void handleDisconnectEdge(EdgeId EId, NodeId NId) {
 223         NodeMetadata& NMd = G.getNodeMetadata(NId);
 224         const MatrixMetadata& MMd = G.getEdgeCosts(EId).getMetadata();
 225         NMd.handleRemoveEdge(MMd, NId == G.getEdgeNode2Id(EId));
 226         if (G.getNodeDegree(NId) == 3) {
 227           // This node is becoming optimally reducible.
 228           moveToOptimallyReducibleNodes(NId);
 229         } else if (NMd.getReductionState() ==
 230                      NodeMetadata::NotProvablyAllocatable &&
 231                    NMd.isConservativelyAllocatable()) {
 232           // This node just became conservatively allocatable.
 233           moveToConservativelyAllocatableNodes(NId);
 234         }
 235       }
 236
 237       void handleReconnectEdge(EdgeId EId, NodeId NId) {
 238         NodeMetadata& NMd = G.getNodeMetadata(NId);
 239         const MatrixMetadata& MMd = G.getEdgeCosts(EId).getMetadata();
 240         NMd.handleAddEdge(MMd, NId == G.getEdgeNode2Id(EId));
 241       }
 242
 243       void handleSetEdgeCosts(EdgeId EId, const Matrix& NewCosts) {
 244         handleRemoveEdge(EId);
 245
 246         NodeId N1Id = G.getEdgeNode1Id(EId);
 247         NodeId N2Id = G.getEdgeNode2Id(EId);
 248         NodeMetadata& N1Md = G.getNodeMetadata(N1Id);
 249         NodeMetadata& N2Md = G.getNodeMetadata(N2Id);
 250         const MatrixMetadata& MMd = NewCosts.getMetadata();
 251         N1Md.handleAddEdge(MMd, N1Id != G.getEdgeNode1Id(EId));
 252         N2Md.handleAddEdge(MMd, N2Id != G.getEdgeNode1Id(EId));
 253       }
 254
 255     private:
 256
 257       void removeFromCurrentSet(NodeId NId) {
 258         switch (G.getNodeMetadata(NId).getReductionState()) {
 259           case NodeMetadata::Unprocessed: break;
 260           case NodeMetadata::OptimallyReducible:
 261             assert(OptimallyReducibleNodes.find(NId) !=
 262                      OptimallyReducibleNodes.end() &&
 263                    "Node not in optimally reducible set.");
 264             OptimallyReducibleNodes.erase(NId);
 265             break;
 266           case NodeMetadata::ConservativelyAllocatable:
 267             assert(ConservativelyAllocatableNodes.find(NId) !=
 268                      ConservativelyAllocatableNodes.end() &&
 269                    "Node not in conservatively allocatable set.");
 270             ConservativelyAllocatableNodes.erase(NId);
 271             break;
 272           case NodeMetadata::NotProvablyAllocatable:
 273             assert(NotProvablyAllocatableNodes.find(NId) !=
 274                      NotProvablyAllocatableNodes.end() &&
 275                    "Node not in not-provably-allocatable set.");
 276             NotProvablyAllocatableNodes.erase(NId);
 277             break;
 278         }
 279       }
 280
 281       void moveToOptimallyReducibleNodes(NodeId NId) {
 282         removeFromCurrentSet(NId);
 283         OptimallyReducibleNodes.insert(NId);
 284         G.getNodeMetadata(NId).setReductionState(
 285           NodeMetadata::OptimallyReducible);
 286       }
 287
 288       void moveToConservativelyAllocatableNodes(NodeId NId) {
 289         removeFromCurrentSet(NId);
 290         ConservativelyAllocatableNodes.insert(NId);
 291         G.getNodeMetadata(NId).setReductionState(
 292           NodeMetadata::ConservativelyAllocatable);
 293       }
 294
 295       void moveToNotProvablyAllocatableNodes(NodeId NId) {
 296         removeFromCurrentSet(NId);
 297         NotProvablyAllocatableNodes.insert(NId);
 298         G.getNodeMetadata(NId).setReductionState(
 299           NodeMetadata::NotProvablyAllocatable);
 300       }
 301
 302       void setup() {
 303         // Set up worklists.
 304         for (auto NId : G.nodeIds()) {
 305           if (G.getNodeDegree(NId) < 3)
 306             moveToOptimallyReducibleNodes(NId);
 307           else if (G.getNodeMetadata(NId).isConservativelyAllocatable())
 308             moveToConservativelyAllocatableNodes(NId);
 309           else
 310             moveToNotProvablyAllocatableNodes(NId);
 311         }
 312       }
 313
 314       // Compute a reduction order for the graph by iteratively applying PBQP
 315       // reduction rules. Locally optimal rules are applied whenever possible (R0,
 316       // R1, R2). If no locally-optimal rules apply then any conservatively
 317       // allocatable node is reduced. Finally, if no conservatively allocatable
 318       // node exists then the node with the lowest spill-cost:degree ratio is
 319       // selected.
 320       std::vector<GraphBase::NodeId> reduce() {
 321         assert(!G.empty() && "Cannot reduce empty graph.");
 322
 323         typedef GraphBase::NodeId NodeId;
 324         std::vector<NodeId> NodeStack;
 325
 326         // Consume worklists.
 327         while (true) {
 328           if (!OptimallyReducibleNodes.empty()) {
 329             NodeSet::iterator NItr = OptimallyReducibleNodes.begin();
 330             NodeId NId = *NItr;
 331             OptimallyReducibleNodes.erase(NItr);
 332             NodeStack.push_back(NId);
 333             switch (G.getNodeDegree(NId)) {
 334               case 0:
 335                 break;
 336               case 1:
 337                 applyR1(G, NId);
 338                 break;
 339               case 2:
 340                 applyR2(G, NId);
 341                 break;
 342               default: llvm_unreachable("Not an optimally reducible node.");
 343             }
 344           } else if (!ConservativelyAllocatableNodes.empty()) {
 345             // Conservatively allocatable nodes will never spill. For now just
 346             // take the first node in the set and push it on the stack. When we
 347             // start optimizing more heavily for register preferencing, it may
 348             // would be better to push nodes with lower 'expected' or worst-case
 349             // register costs first (since early nodes are the most
 350             // constrained).
 351             NodeSet::iterator NItr = ConservativelyAllocatableNodes.begin();
 352             NodeId NId = *NItr;
 353             ConservativelyAllocatableNodes.erase(NItr);
 354             NodeStack.push_back(NId);
 355             G.disconnectAllNeighborsFromNode(NId);
 356
 357           } else if (!NotProvablyAllocatableNodes.empty()) {
 358             NodeSet::iterator NItr =
 359               std::min_element(NotProvablyAllocatableNodes.begin(),
 360                                NotProvablyAllocatableNodes.end(),
 361                                SpillCostComparator(G));
 362             NodeId NId = *NItr;
 363             NotProvablyAllocatableNodes.erase(NItr);
 364             NodeStack.push_back(NId);
 365             G.disconnectAllNeighborsFromNode(NId);
 366           } else
 367             break;
 368         }
 369
 370         return NodeStack;
 371       }
 372
 373       class SpillCostComparator {
 374       public:
 375         SpillCostComparator(const Graph& G) : G(G) {}
 376         bool operator()(NodeId N1Id, NodeId N2Id) {
 377           PBQPNum N1SC = G.getNodeCosts(N1Id)[0] / G.getNodeDegree(N1Id);
 378           PBQPNum N2SC = G.getNodeCosts(N2Id)[0] / G.getNodeDegree(N2Id);
 379           return N1SC < N2SC;
 380         }
 381       private:
 382         const Graph& G;
 383       };
 384
 385       Graph& G;
 386       typedef std::set<NodeId> NodeSet;
 387       NodeSet OptimallyReducibleNodes;
 388       NodeSet ConservativelyAllocatableNodes;
 389       NodeSet NotProvablyAllocatableNodes;
 390     };
 391
 392     class PBQPRAGraph : public PBQP::Graph<RegAllocSolverImpl> {
 393     private:
 394       typedef PBQP::Graph<RegAllocSolverImpl> BaseT;
 395     public:
 396       PBQPRAGraph(GraphMetadata Metadata) : BaseT(Metadata) {}
 397     };
 398
 399     inline Solution solve(PBQPRAGraph& G) {
 400       if (G.empty())
 401         return Solution();
 402       RegAllocSolverImpl RegAllocSolver(G);
 403       return RegAllocSolver.solve();
 404     }
 405   } // namespace RegAlloc
 406 } // namespace PBQP
 407 } // namespace llvm
 408
 409 #endif // LLVM_CODEGEN_PBQP_REGALLOCSOLVER_H