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