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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202735 91177308-0d34-0410-b5e6-96231b3b80d8
360 lines
12 KiB
C++
360 lines
12 KiB
C++
//===-- RegAllocSolver.h - Heuristic PBQP Solver for reg alloc --*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// Heuristic PBQP solver for register allocation problems. This solver uses a
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// graph reduction approach. Nodes of degree 0, 1 and 2 are eliminated with
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// optimality-preserving rules (see ReductionRules.h). When no low-degree (<3)
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// nodes are present, a heuristic derived from Brigg's graph coloring approach
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// is used.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_CODEGEN_PBQP_REGALLOCSOLVER_H
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#define LLVM_CODEGEN_PBQP_REGALLOCSOLVER_H
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#include "CostAllocator.h"
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#include "Graph.h"
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#include "ReductionRules.h"
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#include "Solution.h"
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#include "llvm/Support/ErrorHandling.h"
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#include <limits>
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#include <vector>
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namespace PBQP {
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namespace RegAlloc {
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/// \brief Metadata to speed allocatability test.
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///
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/// Keeps track of the number of infinities in each row and column.
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class MatrixMetadata {
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private:
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MatrixMetadata(const MatrixMetadata&);
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void operator=(const MatrixMetadata&);
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public:
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MatrixMetadata(const PBQP::Matrix& m)
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: worstRow(0), worstCol(0),
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unsafeRows(new bool[m.getRows() - 1]()),
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unsafeCols(new bool[m.getCols() - 1]()) {
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unsigned* colCounts = new unsigned[m.getCols() - 1]();
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for (unsigned i = 1; i < m.getRows(); ++i) {
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unsigned rowCount = 0;
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for (unsigned j = 1; j < m.getCols(); ++j) {
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if (m[i][j] == std::numeric_limits<PBQP::PBQPNum>::infinity()) {
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++rowCount;
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++colCounts[j - 1];
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unsafeRows[i - 1] = true;
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unsafeCols[j - 1] = true;
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}
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}
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worstRow = std::max(worstRow, rowCount);
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}
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unsigned worstColCountForCurRow =
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*std::max_element(colCounts, colCounts + m.getCols() - 1);
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worstCol = std::max(worstCol, worstColCountForCurRow);
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delete[] colCounts;
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}
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~MatrixMetadata() {
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delete[] unsafeRows;
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delete[] unsafeCols;
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}
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unsigned getWorstRow() const { return worstRow; }
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unsigned getWorstCol() const { return worstCol; }
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const bool* getUnsafeRows() const { return unsafeRows; }
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const bool* getUnsafeCols() const { return unsafeCols; }
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private:
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unsigned worstRow, worstCol;
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bool* unsafeRows;
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bool* unsafeCols;
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};
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class NodeMetadata {
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public:
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typedef enum { Unprocessed,
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OptimallyReducible,
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ConservativelyAllocatable,
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NotProvablyAllocatable } ReductionState;
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NodeMetadata() : rs(Unprocessed), deniedOpts(0), optUnsafeEdges(0) {}
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~NodeMetadata() { delete[] optUnsafeEdges; }
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void setup(const Vector& costs) {
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numOpts = costs.getLength() - 1;
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optUnsafeEdges = new unsigned[numOpts]();
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}
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ReductionState getReductionState() const { return rs; }
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void setReductionState(ReductionState rs) { this->rs = rs; }
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void handleAddEdge(const MatrixMetadata& md, bool transpose) {
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deniedOpts += transpose ? md.getWorstCol() : md.getWorstRow();
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const bool* unsafeOpts =
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transpose ? md.getUnsafeCols() : md.getUnsafeRows();
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for (unsigned i = 0; i < numOpts; ++i)
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optUnsafeEdges[i] += unsafeOpts[i];
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}
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void handleRemoveEdge(const MatrixMetadata& md, bool transpose) {
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deniedOpts -= transpose ? md.getWorstCol() : md.getWorstRow();
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const bool* unsafeOpts =
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transpose ? md.getUnsafeCols() : md.getUnsafeRows();
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for (unsigned i = 0; i < numOpts; ++i)
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optUnsafeEdges[i] -= unsafeOpts[i];
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}
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bool isConservativelyAllocatable() const {
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return (deniedOpts < numOpts) ||
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(std::find(optUnsafeEdges, optUnsafeEdges + numOpts, 0) !=
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optUnsafeEdges + numOpts);
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}
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private:
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ReductionState rs;
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unsigned numOpts;
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unsigned deniedOpts;
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unsigned* optUnsafeEdges;
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};
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class RegAllocSolverImpl {
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private:
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typedef PBQP::MDMatrix<MatrixMetadata> RAMatrix;
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public:
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typedef PBQP::Vector RawVector;
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typedef PBQP::Matrix RawMatrix;
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typedef PBQP::Vector Vector;
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typedef RAMatrix Matrix;
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typedef PBQP::PoolCostAllocator<
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Vector, PBQP::VectorComparator,
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Matrix, PBQP::MatrixComparator> CostAllocator;
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typedef PBQP::GraphBase::NodeId NodeId;
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typedef PBQP::GraphBase::EdgeId EdgeId;
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typedef RegAlloc::NodeMetadata NodeMetadata;
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struct EdgeMetadata { };
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typedef PBQP::Graph<RegAllocSolverImpl> Graph;
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RegAllocSolverImpl(Graph &G) : G(G) {}
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Solution solve() {
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G.setSolver(*this);
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Solution S;
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setup();
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S = backpropagate(G, reduce());
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G.unsetSolver();
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return S;
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}
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void handleAddNode(NodeId NId) {
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G.getNodeMetadata(NId).setup(G.getNodeCosts(NId));
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}
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void handleRemoveNode(NodeId NId) {}
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void handleSetNodeCosts(NodeId NId, const Vector& newCosts) {}
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void handleAddEdge(EdgeId EId) {
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handleReconnectEdge(EId, G.getEdgeNode1Id(EId));
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handleReconnectEdge(EId, G.getEdgeNode2Id(EId));
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}
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void handleRemoveEdge(EdgeId EId) {
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handleDisconnectEdge(EId, G.getEdgeNode1Id(EId));
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handleDisconnectEdge(EId, G.getEdgeNode2Id(EId));
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}
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void handleDisconnectEdge(EdgeId EId, NodeId NId) {
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NodeMetadata& nMd = G.getNodeMetadata(NId);
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const MatrixMetadata& mMd = G.getEdgeCosts(EId).getMetadata();
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nMd.handleRemoveEdge(mMd, NId == G.getEdgeNode2Id(EId));
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if (G.getNodeDegree(NId) == 3) {
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// This node is becoming optimally reducible.
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moveToOptimallyReducibleNodes(NId);
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} else if (nMd.getReductionState() ==
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NodeMetadata::NotProvablyAllocatable &&
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nMd.isConservativelyAllocatable()) {
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// This node just became conservatively allocatable.
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moveToConservativelyAllocatableNodes(NId);
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}
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}
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void handleReconnectEdge(EdgeId EId, NodeId NId) {
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NodeMetadata& nMd = G.getNodeMetadata(NId);
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const MatrixMetadata& mMd = G.getEdgeCosts(EId).getMetadata();
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nMd.handleAddEdge(mMd, NId == G.getEdgeNode2Id(EId));
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}
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void handleSetEdgeCosts(EdgeId EId, const Matrix& NewCosts) {
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handleRemoveEdge(EId);
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NodeId n1Id = G.getEdgeNode1Id(EId);
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NodeId n2Id = G.getEdgeNode2Id(EId);
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NodeMetadata& n1Md = G.getNodeMetadata(n1Id);
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NodeMetadata& n2Md = G.getNodeMetadata(n2Id);
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const MatrixMetadata& mMd = NewCosts.getMetadata();
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n1Md.handleAddEdge(mMd, n1Id != G.getEdgeNode1Id(EId));
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n2Md.handleAddEdge(mMd, n2Id != G.getEdgeNode1Id(EId));
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}
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private:
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void removeFromCurrentSet(NodeId NId) {
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switch (G.getNodeMetadata(NId).getReductionState()) {
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case NodeMetadata::Unprocessed: break;
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case NodeMetadata::OptimallyReducible:
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assert(OptimallyReducibleNodes.find(NId) !=
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OptimallyReducibleNodes.end() &&
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"Node not in optimally reducible set.");
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OptimallyReducibleNodes.erase(NId);
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break;
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case NodeMetadata::ConservativelyAllocatable:
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assert(ConservativelyAllocatableNodes.find(NId) !=
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ConservativelyAllocatableNodes.end() &&
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"Node not in conservatively allocatable set.");
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ConservativelyAllocatableNodes.erase(NId);
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break;
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case NodeMetadata::NotProvablyAllocatable:
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assert(NotProvablyAllocatableNodes.find(NId) !=
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NotProvablyAllocatableNodes.end() &&
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"Node not in not-provably-allocatable set.");
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NotProvablyAllocatableNodes.erase(NId);
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break;
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}
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}
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void moveToOptimallyReducibleNodes(NodeId NId) {
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removeFromCurrentSet(NId);
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OptimallyReducibleNodes.insert(NId);
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G.getNodeMetadata(NId).setReductionState(
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NodeMetadata::OptimallyReducible);
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}
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void moveToConservativelyAllocatableNodes(NodeId NId) {
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removeFromCurrentSet(NId);
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ConservativelyAllocatableNodes.insert(NId);
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G.getNodeMetadata(NId).setReductionState(
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NodeMetadata::ConservativelyAllocatable);
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}
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void moveToNotProvablyAllocatableNodes(NodeId NId) {
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removeFromCurrentSet(NId);
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NotProvablyAllocatableNodes.insert(NId);
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G.getNodeMetadata(NId).setReductionState(
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NodeMetadata::NotProvablyAllocatable);
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}
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void setup() {
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// Set up worklists.
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for (auto NId : G.nodeIds()) {
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if (G.getNodeDegree(NId) < 3)
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moveToOptimallyReducibleNodes(NId);
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else if (G.getNodeMetadata(NId).isConservativelyAllocatable())
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moveToConservativelyAllocatableNodes(NId);
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else
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moveToNotProvablyAllocatableNodes(NId);
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}
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}
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// Compute a reduction order for the graph by iteratively applying PBQP
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// reduction rules. Locally optimal rules are applied whenever possible (R0,
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// R1, R2). If no locally-optimal rules apply then any conservatively
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// allocatable node is reduced. Finally, if no conservatively allocatable
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// node exists then the node with the lowest spill-cost:degree ratio is
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// selected.
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std::vector<GraphBase::NodeId> reduce() {
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assert(!G.empty() && "Cannot reduce empty graph.");
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typedef GraphBase::NodeId NodeId;
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std::vector<NodeId> NodeStack;
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// Consume worklists.
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while (true) {
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if (!OptimallyReducibleNodes.empty()) {
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NodeSet::iterator nItr = OptimallyReducibleNodes.begin();
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NodeId NId = *nItr;
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OptimallyReducibleNodes.erase(nItr);
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NodeStack.push_back(NId);
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switch (G.getNodeDegree(NId)) {
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case 0:
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break;
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case 1:
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applyR1(G, NId);
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break;
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case 2:
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applyR2(G, NId);
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break;
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default: llvm_unreachable("Not an optimally reducible node.");
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}
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} else if (!ConservativelyAllocatableNodes.empty()) {
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// Conservatively allocatable nodes will never spill. For now just
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// take the first node in the set and push it on the stack. When we
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// start optimizing more heavily for register preferencing, it may
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// would be better to push nodes with lower 'expected' or worst-case
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// register costs first (since early nodes are the most
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// constrained).
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NodeSet::iterator nItr = ConservativelyAllocatableNodes.begin();
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NodeId NId = *nItr;
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ConservativelyAllocatableNodes.erase(nItr);
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NodeStack.push_back(NId);
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G.disconnectAllNeighborsFromNode(NId);
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} else if (!NotProvablyAllocatableNodes.empty()) {
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NodeSet::iterator nItr =
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std::min_element(NotProvablyAllocatableNodes.begin(),
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NotProvablyAllocatableNodes.end(),
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SpillCostComparator(G));
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NodeId NId = *nItr;
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NotProvablyAllocatableNodes.erase(nItr);
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NodeStack.push_back(NId);
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G.disconnectAllNeighborsFromNode(NId);
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} else
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break;
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}
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return NodeStack;
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}
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class SpillCostComparator {
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public:
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SpillCostComparator(const Graph& G) : G(G) {}
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bool operator()(NodeId N1Id, NodeId N2Id) {
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PBQPNum N1SC = G.getNodeCosts(N1Id)[0] / G.getNodeDegree(N1Id);
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PBQPNum N2SC = G.getNodeCosts(N2Id)[0] / G.getNodeDegree(N2Id);
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return N1SC < N2SC;
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}
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private:
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const Graph& G;
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};
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Graph& G;
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typedef std::set<NodeId> NodeSet;
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NodeSet OptimallyReducibleNodes;
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NodeSet ConservativelyAllocatableNodes;
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NodeSet NotProvablyAllocatableNodes;
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};
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typedef Graph<RegAllocSolverImpl> Graph;
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Solution solve(Graph& G) {
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if (G.empty())
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return Solution();
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RegAllocSolverImpl RegAllocSolver(G);
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return RegAllocSolver.solve();
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}
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}
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}
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#endif // LLVM_CODEGEN_PBQP_REGALLOCSOLVER_H
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