llvm-6502/include/llvm/CodeGen/PBQP/RegAllocSolver.h
2014-04-24 23:14:32 +00:00

360 lines
12 KiB
C++

//===-- 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 PBQP {
namespace RegAlloc {
/// \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 enum { Unprocessed,
OptimallyReducible,
ConservativelyAllocatable,
NotProvablyAllocatable } ReductionState;
NodeMetadata() : RS(Unprocessed), DeniedOpts(0), OptUnsafeEdges(nullptr){}
~NodeMetadata() { delete[] OptUnsafeEdges; }
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;
};
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 { };
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;
};
typedef Graph<RegAllocSolverImpl> Graph;
inline Solution solve(Graph& G) {
if (G.empty())
return Solution();
RegAllocSolverImpl RegAllocSolver(G);
return RegAllocSolver.solve();
}
}
}
#endif // LLVM_CODEGEN_PBQP_REGALLOCSOLVER_H