[PBQP] Move register-allocation specific PBQP code into RegAllocPBQP.h.
authorLang Hames <lhames@gmail.com>
Sat, 18 Oct 2014 22:23:55 +0000 (22:23 +0000)
committerLang Hames <lhames@gmail.com>
Sat, 18 Oct 2014 22:23:55 +0000 (22:23 +0000)
Just clean-up - no functional change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220145 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/PBQP/RegAllocSolver.h [deleted file]
include/llvm/CodeGen/RegAllocPBQP.h

diff --git a/include/llvm/CodeGen/PBQP/RegAllocSolver.h b/include/llvm/CodeGen/PBQP/RegAllocSolver.h
deleted file mode 100644 (file)
index 586d897..0000000
+++ /dev/null
@@ -1,409 +0,0 @@
-//===-- RegAllocSolver.h - Heuristic PBQP Solver for reg alloc --*- C++ -*-===//
-//
-//                     The LLVM Compiler Infrastructure
-//
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
-//
-//===----------------------------------------------------------------------===//
-//
-// Heuristic PBQP solver for register allocation problems. This solver uses a
-// graph reduction approach. Nodes of degree 0, 1 and 2 are eliminated with
-// optimality-preserving rules (see ReductionRules.h). When no low-degree (<3)
-// nodes are present, a heuristic derived from Brigg's graph coloring approach
-// is used.
-//
-//===----------------------------------------------------------------------===//
-
-#ifndef LLVM_CODEGEN_PBQP_REGALLOCSOLVER_H
-#define LLVM_CODEGEN_PBQP_REGALLOCSOLVER_H
-
-#include "CostAllocator.h"
-#include "Graph.h"
-#include "ReductionRules.h"
-#include "Solution.h"
-#include "llvm/Support/ErrorHandling.h"
-#include <limits>
-#include <vector>
-
-namespace llvm{
-namespace PBQP {
-  namespace RegAlloc {
-
-    /// @brief Spill option index.
-    inline unsigned getSpillOptionIdx() { return 0; }
-
-    /// \brief Metadata to speed allocatability test.
-    ///
-    /// Keeps track of the number of infinities in each row and column.
-    class MatrixMetadata {
-    private:
-      MatrixMetadata(const MatrixMetadata&);
-      void operator=(const MatrixMetadata&);
-    public:
-      MatrixMetadata(const PBQP::Matrix& M)
-        : WorstRow(0), WorstCol(0),
-          UnsafeRows(new bool[M.getRows() - 1]()),
-          UnsafeCols(new bool[M.getCols() - 1]()) {
-
-        unsigned* ColCounts = new unsigned[M.getCols() - 1]();
-
-        for (unsigned i = 1; i < M.getRows(); ++i) {
-          unsigned RowCount = 0;
-          for (unsigned j = 1; j < M.getCols(); ++j) {
-            if (M[i][j] == std::numeric_limits<PBQP::PBQPNum>::infinity()) {
-              ++RowCount;
-              ++ColCounts[j - 1];
-              UnsafeRows[i - 1] = true;
-              UnsafeCols[j - 1] = true;
-            }
-          }
-          WorstRow = std::max(WorstRow, RowCount);
-        }
-        unsigned WorstColCountForCurRow =
-          *std::max_element(ColCounts, ColCounts + M.getCols() - 1);
-        WorstCol = std::max(WorstCol, WorstColCountForCurRow);
-        delete[] ColCounts;
-      }
-
-      ~MatrixMetadata() {
-        delete[] UnsafeRows;
-        delete[] UnsafeCols;
-      }
-
-      unsigned getWorstRow() const { return WorstRow; }
-      unsigned getWorstCol() const { return WorstCol; }
-      const bool* getUnsafeRows() const { return UnsafeRows; }
-      const bool* getUnsafeCols() const { return UnsafeCols; }
-
-    private:
-      unsigned WorstRow, WorstCol;
-      bool* UnsafeRows;
-      bool* UnsafeCols;
-    };
-
-    class NodeMetadata {
-    public:
-      typedef std::vector<unsigned> OptionToRegMap;
-
-      typedef enum { Unprocessed,
-                     OptimallyReducible,
-                     ConservativelyAllocatable,
-                     NotProvablyAllocatable } ReductionState;
-
-      NodeMetadata() : RS(Unprocessed), DeniedOpts(0), OptUnsafeEdges(nullptr){}
-      ~NodeMetadata() { delete[] OptUnsafeEdges; }
-
-      void setVReg(unsigned VReg) { this->VReg = VReg; }
-      unsigned getVReg() const { return VReg; }
-
-      void setOptionRegs(OptionToRegMap OptionRegs) {
-        this->OptionRegs = std::move(OptionRegs);
-      }
-      const OptionToRegMap& getOptionRegs() const { return OptionRegs; }
-
-      void setup(const Vector& Costs) {
-        NumOpts = Costs.getLength() - 1;
-        OptUnsafeEdges = new unsigned[NumOpts]();
-      }
-
-      ReductionState getReductionState() const { return RS; }
-      void setReductionState(ReductionState RS) { this->RS = RS; }
-
-      void handleAddEdge(const MatrixMetadata& MD, bool Transpose) {
-        DeniedOpts += Transpose ? MD.getWorstCol() : MD.getWorstRow();
-        const bool* UnsafeOpts =
-          Transpose ? MD.getUnsafeCols() : MD.getUnsafeRows();
-        for (unsigned i = 0; i < NumOpts; ++i)
-          OptUnsafeEdges[i] += UnsafeOpts[i];
-      }
-
-      void handleRemoveEdge(const MatrixMetadata& MD, bool Transpose) {
-        DeniedOpts -= Transpose ? MD.getWorstCol() : MD.getWorstRow();
-        const bool* UnsafeOpts =
-          Transpose ? MD.getUnsafeCols() : MD.getUnsafeRows();
-        for (unsigned i = 0; i < NumOpts; ++i)
-          OptUnsafeEdges[i] -= UnsafeOpts[i];
-      }
-
-      bool isConservativelyAllocatable() const {
-        return (DeniedOpts < NumOpts) ||
-               (std::find(OptUnsafeEdges, OptUnsafeEdges + NumOpts, 0) !=
-                  OptUnsafeEdges + NumOpts);
-      }
-
-    private:
-      ReductionState RS;
-      unsigned NumOpts;
-      unsigned DeniedOpts;
-      unsigned* OptUnsafeEdges;
-      unsigned VReg;
-      OptionToRegMap OptionRegs;
-    };
-
-    class RegAllocSolverImpl {
-    private:
-      typedef PBQP::MDMatrix<MatrixMetadata> RAMatrix;
-    public:
-      typedef PBQP::Vector RawVector;
-      typedef PBQP::Matrix RawMatrix;
-      typedef PBQP::Vector Vector;
-      typedef RAMatrix     Matrix;
-      typedef PBQP::PoolCostAllocator<
-                Vector, PBQP::VectorComparator,
-                Matrix, PBQP::MatrixComparator> CostAllocator;
-
-      typedef PBQP::GraphBase::NodeId NodeId;
-      typedef PBQP::GraphBase::EdgeId EdgeId;
-
-      typedef RegAlloc::NodeMetadata NodeMetadata;
-
-      struct EdgeMetadata { };
-
-      class GraphMetadata {
-      public:
-        GraphMetadata(MachineFunction &MF,
-                      LiveIntervals &LIS,
-                      MachineBlockFrequencyInfo &MBFI)
-          : MF(MF), LIS(LIS), MBFI(MBFI) {}
-
-        MachineFunction &MF;
-        LiveIntervals &LIS;
-        MachineBlockFrequencyInfo &MBFI;
-
-        void setNodeIdForVReg(unsigned VReg, GraphBase::NodeId NId) {
-          VRegToNodeId[VReg] = NId;
-        }
-
-        GraphBase::NodeId getNodeIdForVReg(unsigned VReg) const {
-          auto VRegItr = VRegToNodeId.find(VReg);
-          if (VRegItr == VRegToNodeId.end())
-            return GraphBase::invalidNodeId();
-          return VRegItr->second;
-        }
-
-        void eraseNodeIdForVReg(unsigned VReg) {
-          VRegToNodeId.erase(VReg);
-        }
-
-      private:
-        DenseMap<unsigned, NodeId> VRegToNodeId;
-      };
-
-      typedef PBQP::Graph<RegAllocSolverImpl> Graph;
-
-      RegAllocSolverImpl(Graph &G) : G(G) {}
-
-      Solution solve() {
-        G.setSolver(*this);
-        Solution S;
-        setup();
-        S = backpropagate(G, reduce());
-        G.unsetSolver();
-        return S;
-      }
-
-      void handleAddNode(NodeId NId) {
-        G.getNodeMetadata(NId).setup(G.getNodeCosts(NId));
-      }
-      void handleRemoveNode(NodeId NId) {}
-      void handleSetNodeCosts(NodeId NId, const Vector& newCosts) {}
-
-      void handleAddEdge(EdgeId EId) {
-        handleReconnectEdge(EId, G.getEdgeNode1Id(EId));
-        handleReconnectEdge(EId, G.getEdgeNode2Id(EId));
-      }
-
-      void handleRemoveEdge(EdgeId EId) {
-        handleDisconnectEdge(EId, G.getEdgeNode1Id(EId));
-        handleDisconnectEdge(EId, G.getEdgeNode2Id(EId));
-      }
-
-      void handleDisconnectEdge(EdgeId EId, NodeId NId) {
-        NodeMetadata& NMd = G.getNodeMetadata(NId);
-        const MatrixMetadata& MMd = G.getEdgeCosts(EId).getMetadata();
-        NMd.handleRemoveEdge(MMd, NId == G.getEdgeNode2Id(EId));
-        if (G.getNodeDegree(NId) == 3) {
-          // This node is becoming optimally reducible.
-          moveToOptimallyReducibleNodes(NId);
-        } else if (NMd.getReductionState() ==
-                     NodeMetadata::NotProvablyAllocatable &&
-                   NMd.isConservativelyAllocatable()) {
-          // This node just became conservatively allocatable.
-          moveToConservativelyAllocatableNodes(NId);
-        }
-      }
-
-      void handleReconnectEdge(EdgeId EId, NodeId NId) {
-        NodeMetadata& NMd = G.getNodeMetadata(NId);
-        const MatrixMetadata& MMd = G.getEdgeCosts(EId).getMetadata();
-        NMd.handleAddEdge(MMd, NId == G.getEdgeNode2Id(EId));
-      }
-
-      void handleSetEdgeCosts(EdgeId EId, const Matrix& NewCosts) {
-        handleRemoveEdge(EId);
-
-        NodeId N1Id = G.getEdgeNode1Id(EId);
-        NodeId N2Id = G.getEdgeNode2Id(EId);
-        NodeMetadata& N1Md = G.getNodeMetadata(N1Id);
-        NodeMetadata& N2Md = G.getNodeMetadata(N2Id);
-        const MatrixMetadata& MMd = NewCosts.getMetadata();
-        N1Md.handleAddEdge(MMd, N1Id != G.getEdgeNode1Id(EId));
-        N2Md.handleAddEdge(MMd, N2Id != G.getEdgeNode1Id(EId));
-      }
-
-    private:
-
-      void removeFromCurrentSet(NodeId NId) {
-        switch (G.getNodeMetadata(NId).getReductionState()) {
-          case NodeMetadata::Unprocessed: break;
-          case NodeMetadata::OptimallyReducible:
-            assert(OptimallyReducibleNodes.find(NId) !=
-                     OptimallyReducibleNodes.end() &&
-                   "Node not in optimally reducible set.");
-            OptimallyReducibleNodes.erase(NId);
-            break;
-          case NodeMetadata::ConservativelyAllocatable:
-            assert(ConservativelyAllocatableNodes.find(NId) !=
-                     ConservativelyAllocatableNodes.end() &&
-                   "Node not in conservatively allocatable set.");
-            ConservativelyAllocatableNodes.erase(NId);
-            break;
-          case NodeMetadata::NotProvablyAllocatable:
-            assert(NotProvablyAllocatableNodes.find(NId) !=
-                     NotProvablyAllocatableNodes.end() &&
-                   "Node not in not-provably-allocatable set.");
-            NotProvablyAllocatableNodes.erase(NId);
-            break;
-        }
-      }
-
-      void moveToOptimallyReducibleNodes(NodeId NId) {
-        removeFromCurrentSet(NId);
-        OptimallyReducibleNodes.insert(NId);
-        G.getNodeMetadata(NId).setReductionState(
-          NodeMetadata::OptimallyReducible);
-      }
-
-      void moveToConservativelyAllocatableNodes(NodeId NId) {
-        removeFromCurrentSet(NId);
-        ConservativelyAllocatableNodes.insert(NId);
-        G.getNodeMetadata(NId).setReductionState(
-          NodeMetadata::ConservativelyAllocatable);
-      }
-
-      void moveToNotProvablyAllocatableNodes(NodeId NId) {
-        removeFromCurrentSet(NId);
-        NotProvablyAllocatableNodes.insert(NId);
-        G.getNodeMetadata(NId).setReductionState(
-          NodeMetadata::NotProvablyAllocatable);
-      }
-
-      void setup() {
-        // Set up worklists.
-        for (auto NId : G.nodeIds()) {
-          if (G.getNodeDegree(NId) < 3)
-            moveToOptimallyReducibleNodes(NId);
-          else if (G.getNodeMetadata(NId).isConservativelyAllocatable())
-            moveToConservativelyAllocatableNodes(NId);
-          else
-            moveToNotProvablyAllocatableNodes(NId);
-        }
-      }
-
-      // Compute a reduction order for the graph by iteratively applying PBQP
-      // reduction rules. Locally optimal rules are applied whenever possible (R0,
-      // R1, R2). If no locally-optimal rules apply then any conservatively
-      // allocatable node is reduced. Finally, if no conservatively allocatable
-      // node exists then the node with the lowest spill-cost:degree ratio is
-      // selected.
-      std::vector<GraphBase::NodeId> reduce() {
-        assert(!G.empty() && "Cannot reduce empty graph.");
-
-        typedef GraphBase::NodeId NodeId;
-        std::vector<NodeId> NodeStack;
-
-        // Consume worklists.
-        while (true) {
-          if (!OptimallyReducibleNodes.empty()) {
-            NodeSet::iterator NItr = OptimallyReducibleNodes.begin();
-            NodeId NId = *NItr;
-            OptimallyReducibleNodes.erase(NItr);
-            NodeStack.push_back(NId);
-            switch (G.getNodeDegree(NId)) {
-              case 0:
-                break;
-              case 1:
-                applyR1(G, NId);
-                break;
-              case 2:
-                applyR2(G, NId);
-                break;
-              default: llvm_unreachable("Not an optimally reducible node.");
-            }
-          } else if (!ConservativelyAllocatableNodes.empty()) {
-            // Conservatively allocatable nodes will never spill. For now just
-            // take the first node in the set and push it on the stack. When we
-            // start optimizing more heavily for register preferencing, it may
-            // would be better to push nodes with lower 'expected' or worst-case
-            // register costs first (since early nodes are the most
-            // constrained).
-            NodeSet::iterator NItr = ConservativelyAllocatableNodes.begin();
-            NodeId NId = *NItr;
-            ConservativelyAllocatableNodes.erase(NItr);
-            NodeStack.push_back(NId);
-            G.disconnectAllNeighborsFromNode(NId);
-
-          } else if (!NotProvablyAllocatableNodes.empty()) {
-            NodeSet::iterator NItr =
-              std::min_element(NotProvablyAllocatableNodes.begin(),
-                               NotProvablyAllocatableNodes.end(),
-                               SpillCostComparator(G));
-            NodeId NId = *NItr;
-            NotProvablyAllocatableNodes.erase(NItr);
-            NodeStack.push_back(NId);
-            G.disconnectAllNeighborsFromNode(NId);
-          } else
-            break;
-        }
-
-        return NodeStack;
-      }
-
-      class SpillCostComparator {
-      public:
-        SpillCostComparator(const Graph& G) : G(G) {}
-        bool operator()(NodeId N1Id, NodeId N2Id) {
-          PBQPNum N1SC = G.getNodeCosts(N1Id)[0] / G.getNodeDegree(N1Id);
-          PBQPNum N2SC = G.getNodeCosts(N2Id)[0] / G.getNodeDegree(N2Id);
-          return N1SC < N2SC;
-        }
-      private:
-        const Graph& G;
-      };
-
-      Graph& G;
-      typedef std::set<NodeId> NodeSet;
-      NodeSet OptimallyReducibleNodes;
-      NodeSet ConservativelyAllocatableNodes;
-      NodeSet NotProvablyAllocatableNodes;
-    };
-
-    class PBQPRAGraph : public PBQP::Graph<RegAllocSolverImpl> {
-    private:
-      typedef PBQP::Graph<RegAllocSolverImpl> BaseT;
-    public:
-      PBQPRAGraph(GraphMetadata Metadata) : BaseT(Metadata) {}
-    };
-
-    inline Solution solve(PBQPRAGraph& G) {
-      if (G.empty())
-        return Solution();
-      RegAllocSolverImpl RegAllocSolver(G);
-      return RegAllocSolver.solve();
-    }
-  } // namespace RegAlloc
-} // namespace PBQP
-} // namespace llvm
-
-#endif // LLVM_CODEGEN_PBQP_REGALLOCSOLVER_H
index 93aca3c..6ab9bcc 100644 (file)
 
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/PBQPRAConstraint.h"
-#include "llvm/CodeGen/PBQP/RegAllocSolver.h"
+#include "llvm/CodeGen/PBQP/CostAllocator.h"
+#include "llvm/CodeGen/PBQP/ReductionRules.h"
+#include "llvm/Support/ErrorHandling.h"
 
 namespace llvm {
+namespace PBQP {
+namespace RegAlloc {
 
-  /// @brief Create a PBQP register allocator instance.
-  FunctionPass *
-  createPBQPRegisterAllocator(char *customPassID = nullptr);
+/// @brief Spill option index.
+inline unsigned getSpillOptionIdx() { return 0; }
+
+/// \brief Metadata to speed allocatability test.
+///
+/// Keeps track of the number of infinities in each row and column.
+class MatrixMetadata {
+private:
+  MatrixMetadata(const MatrixMetadata&);
+  void operator=(const MatrixMetadata&);
+public:
+  MatrixMetadata(const Matrix& M)
+    : WorstRow(0), WorstCol(0),
+      UnsafeRows(new bool[M.getRows() - 1]()),
+      UnsafeCols(new bool[M.getCols() - 1]()) {
+
+    unsigned* ColCounts = new unsigned[M.getCols() - 1]();
+
+    for (unsigned i = 1; i < M.getRows(); ++i) {
+      unsigned RowCount = 0;
+      for (unsigned j = 1; j < M.getCols(); ++j) {
+        if (M[i][j] == std::numeric_limits<PBQPNum>::infinity()) {
+          ++RowCount;
+          ++ColCounts[j - 1];
+          UnsafeRows[i - 1] = true;
+          UnsafeCols[j - 1] = true;
+        }
+      }
+      WorstRow = std::max(WorstRow, RowCount);
+    }
+    unsigned WorstColCountForCurRow =
+      *std::max_element(ColCounts, ColCounts + M.getCols() - 1);
+    WorstCol = std::max(WorstCol, WorstColCountForCurRow);
+    delete[] ColCounts;
+  }
+
+  ~MatrixMetadata() {
+    delete[] UnsafeRows;
+    delete[] UnsafeCols;
+  }
+
+  unsigned getWorstRow() const { return WorstRow; }
+  unsigned getWorstCol() const { return WorstCol; }
+  const bool* getUnsafeRows() const { return UnsafeRows; }
+  const bool* getUnsafeCols() const { return UnsafeCols; }
+
+private:
+  unsigned WorstRow, WorstCol;
+  bool* UnsafeRows;
+  bool* UnsafeCols;
+};
+
+class NodeMetadata {
+public:
+  typedef std::vector<unsigned> OptionToRegMap;
+
+  typedef enum { Unprocessed,
+                 OptimallyReducible,
+                 ConservativelyAllocatable,
+                 NotProvablyAllocatable } ReductionState;
+
+  NodeMetadata() : RS(Unprocessed), DeniedOpts(0), OptUnsafeEdges(nullptr){}
+  ~NodeMetadata() { delete[] OptUnsafeEdges; }
+
+  void setVReg(unsigned VReg) { this->VReg = VReg; }
+  unsigned getVReg() const { return VReg; }
+
+  void setOptionRegs(OptionToRegMap OptionRegs) {
+    this->OptionRegs = std::move(OptionRegs);
+  }
+  const OptionToRegMap& getOptionRegs() const { return OptionRegs; }
+
+  void setup(const Vector& Costs) {
+    NumOpts = Costs.getLength() - 1;
+    OptUnsafeEdges = new unsigned[NumOpts]();
+  }
+
+  ReductionState getReductionState() const { return RS; }
+  void setReductionState(ReductionState RS) { this->RS = RS; }
+
+  void handleAddEdge(const MatrixMetadata& MD, bool Transpose) {
+    DeniedOpts += Transpose ? MD.getWorstCol() : MD.getWorstRow();
+    const bool* UnsafeOpts =
+      Transpose ? MD.getUnsafeCols() : MD.getUnsafeRows();
+    for (unsigned i = 0; i < NumOpts; ++i)
+      OptUnsafeEdges[i] += UnsafeOpts[i];
+  }
+
+  void handleRemoveEdge(const MatrixMetadata& MD, bool Transpose) {
+    DeniedOpts -= Transpose ? MD.getWorstCol() : MD.getWorstRow();
+    const bool* UnsafeOpts =
+      Transpose ? MD.getUnsafeCols() : MD.getUnsafeRows();
+    for (unsigned i = 0; i < NumOpts; ++i)
+      OptUnsafeEdges[i] -= UnsafeOpts[i];
+  }
+
+  bool isConservativelyAllocatable() const {
+    return (DeniedOpts < NumOpts) ||
+      (std::find(OptUnsafeEdges, OptUnsafeEdges + NumOpts, 0) !=
+       OptUnsafeEdges + NumOpts);
+  }
+
+private:
+  ReductionState RS;
+  unsigned NumOpts;
+  unsigned DeniedOpts;
+  unsigned* OptUnsafeEdges;
+  unsigned VReg;
+  OptionToRegMap OptionRegs;
+};
+
+class RegAllocSolverImpl {
+private:
+  typedef MDMatrix<MatrixMetadata> RAMatrix;
+public:
+  typedef PBQP::Vector RawVector;
+  typedef PBQP::Matrix RawMatrix;
+  typedef PBQP::Vector Vector;
+  typedef RAMatrix     Matrix;
+  typedef PBQP::PoolCostAllocator<
+    Vector, PBQP::VectorComparator,
+    Matrix, PBQP::MatrixComparator> CostAllocator;
+
+  typedef GraphBase::NodeId NodeId;
+  typedef GraphBase::EdgeId EdgeId;
+
+  typedef RegAlloc::NodeMetadata NodeMetadata;
+
+  struct EdgeMetadata { };
+
+  class GraphMetadata {
+  public:
+    GraphMetadata(MachineFunction &MF,
+                  LiveIntervals &LIS,
+                  MachineBlockFrequencyInfo &MBFI)
+      : MF(MF), LIS(LIS), MBFI(MBFI) {}
+
+    MachineFunction &MF;
+    LiveIntervals &LIS;
+    MachineBlockFrequencyInfo &MBFI;
+
+    void setNodeIdForVReg(unsigned VReg, GraphBase::NodeId NId) {
+      VRegToNodeId[VReg] = NId;
+    }
+
+    GraphBase::NodeId getNodeIdForVReg(unsigned VReg) const {
+      auto VRegItr = VRegToNodeId.find(VReg);
+      if (VRegItr == VRegToNodeId.end())
+        return GraphBase::invalidNodeId();
+      return VRegItr->second;
+    }
+
+    void eraseNodeIdForVReg(unsigned VReg) {
+      VRegToNodeId.erase(VReg);
+    }
+
+  private:
+    DenseMap<unsigned, NodeId> VRegToNodeId;
+  };
+
+  typedef PBQP::Graph<RegAllocSolverImpl> Graph;
+
+  RegAllocSolverImpl(Graph &G) : G(G) {}
+
+  Solution solve() {
+    G.setSolver(*this);
+    Solution S;
+    setup();
+    S = backpropagate(G, reduce());
+    G.unsetSolver();
+    return S;
+  }
+
+  void handleAddNode(NodeId NId) {
+    G.getNodeMetadata(NId).setup(G.getNodeCosts(NId));
+  }
+  void handleRemoveNode(NodeId NId) {}
+  void handleSetNodeCosts(NodeId NId, const Vector& newCosts) {}
+
+  void handleAddEdge(EdgeId EId) {
+    handleReconnectEdge(EId, G.getEdgeNode1Id(EId));
+    handleReconnectEdge(EId, G.getEdgeNode2Id(EId));
+  }
+
+  void handleRemoveEdge(EdgeId EId) {
+    handleDisconnectEdge(EId, G.getEdgeNode1Id(EId));
+    handleDisconnectEdge(EId, G.getEdgeNode2Id(EId));
+  }
+
+  void handleDisconnectEdge(EdgeId EId, NodeId NId) {
+    NodeMetadata& NMd = G.getNodeMetadata(NId);
+    const MatrixMetadata& MMd = G.getEdgeCosts(EId).getMetadata();
+    NMd.handleRemoveEdge(MMd, NId == G.getEdgeNode2Id(EId));
+    if (G.getNodeDegree(NId) == 3) {
+      // This node is becoming optimally reducible.
+      moveToOptimallyReducibleNodes(NId);
+    } else if (NMd.getReductionState() ==
+               NodeMetadata::NotProvablyAllocatable &&
+               NMd.isConservativelyAllocatable()) {
+      // This node just became conservatively allocatable.
+      moveToConservativelyAllocatableNodes(NId);
+    }
+  }
+
+  void handleReconnectEdge(EdgeId EId, NodeId NId) {
+    NodeMetadata& NMd = G.getNodeMetadata(NId);
+    const MatrixMetadata& MMd = G.getEdgeCosts(EId).getMetadata();
+    NMd.handleAddEdge(MMd, NId == G.getEdgeNode2Id(EId));
+  }
+
+  void handleSetEdgeCosts(EdgeId EId, const Matrix& NewCosts) {
+    handleRemoveEdge(EId);
+
+    NodeId N1Id = G.getEdgeNode1Id(EId);
+    NodeId N2Id = G.getEdgeNode2Id(EId);
+    NodeMetadata& N1Md = G.getNodeMetadata(N1Id);
+    NodeMetadata& N2Md = G.getNodeMetadata(N2Id);
+    const MatrixMetadata& MMd = NewCosts.getMetadata();
+    N1Md.handleAddEdge(MMd, N1Id != G.getEdgeNode1Id(EId));
+    N2Md.handleAddEdge(MMd, N2Id != G.getEdgeNode1Id(EId));
+  }
+
+private:
+
+  void removeFromCurrentSet(NodeId NId) {
+    switch (G.getNodeMetadata(NId).getReductionState()) {
+    case NodeMetadata::Unprocessed: break;
+    case NodeMetadata::OptimallyReducible:
+      assert(OptimallyReducibleNodes.find(NId) !=
+             OptimallyReducibleNodes.end() &&
+             "Node not in optimally reducible set.");
+      OptimallyReducibleNodes.erase(NId);
+      break;
+    case NodeMetadata::ConservativelyAllocatable:
+      assert(ConservativelyAllocatableNodes.find(NId) !=
+             ConservativelyAllocatableNodes.end() &&
+             "Node not in conservatively allocatable set.");
+      ConservativelyAllocatableNodes.erase(NId);
+      break;
+    case NodeMetadata::NotProvablyAllocatable:
+      assert(NotProvablyAllocatableNodes.find(NId) !=
+             NotProvablyAllocatableNodes.end() &&
+             "Node not in not-provably-allocatable set.");
+      NotProvablyAllocatableNodes.erase(NId);
+      break;
+    }
+  }
+
+  void moveToOptimallyReducibleNodes(NodeId NId) {
+    removeFromCurrentSet(NId);
+    OptimallyReducibleNodes.insert(NId);
+    G.getNodeMetadata(NId).setReductionState(
+      NodeMetadata::OptimallyReducible);
+  }
+
+  void moveToConservativelyAllocatableNodes(NodeId NId) {
+    removeFromCurrentSet(NId);
+    ConservativelyAllocatableNodes.insert(NId);
+    G.getNodeMetadata(NId).setReductionState(
+      NodeMetadata::ConservativelyAllocatable);
+  }
+
+  void moveToNotProvablyAllocatableNodes(NodeId NId) {
+    removeFromCurrentSet(NId);
+    NotProvablyAllocatableNodes.insert(NId);
+    G.getNodeMetadata(NId).setReductionState(
+      NodeMetadata::NotProvablyAllocatable);
+  }
+
+  void setup() {
+    // Set up worklists.
+    for (auto NId : G.nodeIds()) {
+      if (G.getNodeDegree(NId) < 3)
+        moveToOptimallyReducibleNodes(NId);
+      else if (G.getNodeMetadata(NId).isConservativelyAllocatable())
+        moveToConservativelyAllocatableNodes(NId);
+      else
+        moveToNotProvablyAllocatableNodes(NId);
+    }
+  }
+
+  // Compute a reduction order for the graph by iteratively applying PBQP
+  // reduction rules. Locally optimal rules are applied whenever possible (R0,
+  // R1, R2). If no locally-optimal rules apply then any conservatively
+  // allocatable node is reduced. Finally, if no conservatively allocatable
+  // node exists then the node with the lowest spill-cost:degree ratio is
+  // selected.
+  std::vector<GraphBase::NodeId> reduce() {
+    assert(!G.empty() && "Cannot reduce empty graph.");
+
+    typedef GraphBase::NodeId NodeId;
+    std::vector<NodeId> NodeStack;
+
+    // Consume worklists.
+    while (true) {
+      if (!OptimallyReducibleNodes.empty()) {
+        NodeSet::iterator NItr = OptimallyReducibleNodes.begin();
+        NodeId NId = *NItr;
+        OptimallyReducibleNodes.erase(NItr);
+        NodeStack.push_back(NId);
+        switch (G.getNodeDegree(NId)) {
+        case 0:
+          break;
+        case 1:
+          applyR1(G, NId);
+          break;
+        case 2:
+          applyR2(G, NId);
+          break;
+        default: llvm_unreachable("Not an optimally reducible node.");
+        }
+      } else if (!ConservativelyAllocatableNodes.empty()) {
+        // Conservatively allocatable nodes will never spill. For now just
+        // take the first node in the set and push it on the stack. When we
+        // start optimizing more heavily for register preferencing, it may
+        // would be better to push nodes with lower 'expected' or worst-case
+        // register costs first (since early nodes are the most
+        // constrained).
+        NodeSet::iterator NItr = ConservativelyAllocatableNodes.begin();
+        NodeId NId = *NItr;
+        ConservativelyAllocatableNodes.erase(NItr);
+        NodeStack.push_back(NId);
+        G.disconnectAllNeighborsFromNode(NId);
+
+      } else if (!NotProvablyAllocatableNodes.empty()) {
+        NodeSet::iterator NItr =
+          std::min_element(NotProvablyAllocatableNodes.begin(),
+                           NotProvablyAllocatableNodes.end(),
+                           SpillCostComparator(G));
+        NodeId NId = *NItr;
+        NotProvablyAllocatableNodes.erase(NItr);
+        NodeStack.push_back(NId);
+        G.disconnectAllNeighborsFromNode(NId);
+      } else
+        break;
+    }
+
+    return NodeStack;
+  }
+
+  class SpillCostComparator {
+  public:
+    SpillCostComparator(const Graph& G) : G(G) {}
+    bool operator()(NodeId N1Id, NodeId N2Id) {
+      PBQPNum N1SC = G.getNodeCosts(N1Id)[0] / G.getNodeDegree(N1Id);
+      PBQPNum N2SC = G.getNodeCosts(N2Id)[0] / G.getNodeDegree(N2Id);
+      return N1SC < N2SC;
+    }
+  private:
+    const Graph& G;
+  };
+
+  Graph& G;
+  typedef std::set<NodeId> NodeSet;
+  NodeSet OptimallyReducibleNodes;
+  NodeSet ConservativelyAllocatableNodes;
+  NodeSet NotProvablyAllocatableNodes;
+};
+
+class PBQPRAGraph : public PBQP::Graph<RegAllocSolverImpl> {
+private:
+  typedef PBQP::Graph<RegAllocSolverImpl> BaseT;
+public:
+  PBQPRAGraph(GraphMetadata Metadata) : BaseT(Metadata) {}
+};
+
+inline Solution solve(PBQPRAGraph& G) {
+  if (G.empty())
+    return Solution();
+  RegAllocSolverImpl RegAllocSolver(G);
+  return RegAllocSolver.solve();
 }
 
+} // namespace RegAlloc
+} // namespace PBQP
+
+/// @brief Create a PBQP register allocator instance.
+FunctionPass *
+createPBQPRegisterAllocator(char *customPassID = nullptr);
+
+} // namespace llvm
+
 #endif /* LLVM_CODEGEN_REGALLOCPBQP_H */