//===- RegAllocPBQP.h -------------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file defines the PBQPBuilder interface, for classes which build PBQP
// instances to represent register allocation problems, and the RegAllocPBQP
// interface.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_CODEGEN_REGALLOCPBQP_H
#define LLVM_CODEGEN_REGALLOCPBQP_H
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/Hashing.h"
#include "llvm/CodeGen/PBQP/CostAllocator.h"
#include "llvm/CodeGen/PBQP/Graph.h"
#include "llvm/CodeGen/PBQP/Math.h"
#include "llvm/CodeGen/PBQP/ReductionRules.h"
#include "llvm/CodeGen/PBQP/Solution.h"
#include "llvm/CodeGen/Register.h"
#include "llvm/MC/MCRegister.h"
#include "llvm/Support/ErrorHandling.h"
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <limits>
#include <memory>
#include <set>
#include <vector>
namespace llvm {
class FunctionPass;
class LiveIntervals;
class MachineBlockFrequencyInfo;
class MachineFunction;
class raw_ostream;
namespace PBQP {
namespace RegAlloc {
/// Spill option index.
inline unsigned getSpillOptionIdx() { return 0; }
/// Metadata to speed allocatability test.
///
/// Keeps track of the number of infinities in each row and column.
class MatrixMetadata {
public:
MatrixMetadata(const Matrix& M)
: 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(const MatrixMetadata &) = delete;
MatrixMetadata &operator=(const MatrixMetadata &) = delete;
unsigned getWorstRow() const { return WorstRow; }
unsigned getWorstCol() const { return WorstCol; }
const bool* getUnsafeRows() const { return UnsafeRows.get(); }
const bool* getUnsafeCols() const { return UnsafeCols.get(); }
private:
unsigned WorstRow = 0;
unsigned WorstCol = 0;
std::unique_ptr<bool[]> UnsafeRows;
std::unique_ptr<bool[]> UnsafeCols;
};
/// Holds a vector of the allowed physical regs for a vreg.
class AllowedRegVector {
friend hash_code hash_value(const AllowedRegVector &);
public:
AllowedRegVector() = default;
AllowedRegVector(AllowedRegVector &&) = default;
AllowedRegVector(const std::vector<MCRegister> &OptVec)
: NumOpts(OptVec.size()), Opts(new MCRegister[NumOpts]) {
std::copy(OptVec.begin(), OptVec.end(), Opts.get());
}
unsigned size() const { return NumOpts; }
MCRegister operator[](size_t I) const { return Opts[I]; }
bool operator==(const AllowedRegVector &Other) const {
if (NumOpts != Other.NumOpts)
return false;
return std::equal(Opts.get(), Opts.get() + NumOpts, Other.Opts.get());
}
bool operator!=(const AllowedRegVector &Other) const {
return !(*this == Other);
}
private:
unsigned NumOpts = 0;
std::unique_ptr<MCRegister[]> Opts;
};
inline hash_code hash_value(const AllowedRegVector &OptRegs) {
MCRegister *OStart = OptRegs.Opts.get();
MCRegister *OEnd = OptRegs.Opts.get() + OptRegs.NumOpts;
return hash_combine(OptRegs.NumOpts,
hash_combine_range(OStart, OEnd));
}
/// Holds graph-level metadata relevant to PBQP RA problems.
class GraphMetadata {
private:
using AllowedRegVecPool = ValuePool<AllowedRegVector>;
public:
using AllowedRegVecRef = AllowedRegVecPool::PoolRef;
GraphMetadata(MachineFunction &MF,
LiveIntervals &LIS,
MachineBlockFrequencyInfo &MBFI)
: MF(MF), LIS(LIS), MBFI(MBFI) {}
MachineFunction &MF;
LiveIntervals &LIS;
MachineBlockFrequencyInfo &MBFI;
void setNodeIdForVReg(Register VReg, GraphBase::NodeId NId) {
VRegToNodeId[VReg.id()] = NId;
}
GraphBase::NodeId getNodeIdForVReg(Register VReg) const {
auto VRegItr = VRegToNodeId.find(VReg);
if (VRegItr == VRegToNodeId.end())
return GraphBase::invalidNodeId();
return VRegItr->second;
}
AllowedRegVecRef getAllowedRegs(AllowedRegVector Allowed) {
return AllowedRegVecs.getValue(std::move(Allowed));
}
private:
DenseMap<Register, GraphBase::NodeId> VRegToNodeId;
AllowedRegVecPool AllowedRegVecs;
};
/// Holds solver state and other metadata relevant to each PBQP RA node.
class NodeMetadata {
public:
using AllowedRegVector = RegAlloc::AllowedRegVector;
// The node's reduction state. The order in this enum is important,
// as it is assumed nodes can only progress up (i.e. towards being
// optimally reducible) when reducing the graph.
using ReductionState = enum {
Unprocessed,
NotProvablyAllocatable,
ConservativelyAllocatable,
OptimallyReducible
};
NodeMetadata() = default;
NodeMetadata(const NodeMetadata &Other)
: RS(Other.RS), NumOpts(Other.NumOpts), DeniedOpts(Other.DeniedOpts),
OptUnsafeEdges(new unsigned[NumOpts]), VReg(Other.VReg),
AllowedRegs(Other.AllowedRegs)
#if LLVM_ENABLE_ABI_BREAKING_CHECKS
,
everConservativelyAllocatable(Other.everConservativelyAllocatable)
#endif
{
if (NumOpts > 0) {
std::copy(&Other.OptUnsafeEdges[0], &Other.OptUnsafeEdges[NumOpts],
&OptUnsafeEdges[0]);
}
}
NodeMetadata(NodeMetadata &&) = default;
NodeMetadata& operator=(NodeMetadata &&) = default;
void setVReg(Register VReg) { this->VReg = VReg; }
Register getVReg() const { return VReg; }
void setAllowedRegs(GraphMetadata::AllowedRegVecRef AllowedRegs) {
this->AllowedRegs = std::move(AllowedRegs);
}
const AllowedRegVector& getAllowedRegs() const { return *AllowedRegs; }
void setup(const Vector& Costs) {
NumOpts = Costs.getLength() - 1;
OptUnsafeEdges = std::unique_ptr<unsigned[]>(new unsigned[NumOpts]());
}
ReductionState getReductionState() const { return RS; }
void setReductionState(ReductionState RS) {
assert(RS >= this->RS && "A node's reduction state can not be downgraded");
this->RS = RS;
#if LLVM_ENABLE_ABI_BREAKING_CHECKS
// Remember this state to assert later that a non-infinite register
// option was available.
if (RS == ConservativelyAllocatable)
everConservativelyAllocatable = true;
#endif
}
void handleAddEdge(const MatrixMetadata& MD, bool Transpose) {
DeniedOpts += Transpose ? MD.getWorstRow() : MD.getWorstCol();
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.getWorstRow() : MD.getWorstCol();
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[0], &OptUnsafeEdges[NumOpts], 0) !=
&OptUnsafeEdges[NumOpts]);
}
#if LLVM_ENABLE_ABI_BREAKING_CHECKS
bool wasConservativelyAllocatable() const {
return everConservativelyAllocatable;
}
#endif
private:
ReductionState RS = Unprocessed;
unsigned NumOpts = 0;
unsigned DeniedOpts = 0;
std::unique_ptr<unsigned[]> OptUnsafeEdges;
Register VReg;
GraphMetadata::AllowedRegVecRef AllowedRegs;
#if LLVM_ENABLE_ABI_BREAKING_CHECKS
bool everConservativelyAllocatable = false;
#endif
};
class RegAllocSolverImpl {
private:
using RAMatrix = MDMatrix<MatrixMetadata>;
public:
using RawVector = PBQP::Vector;
using RawMatrix = PBQP::Matrix;
using Vector = PBQP::Vector;
using Matrix = RAMatrix;
using CostAllocator = PBQP::PoolCostAllocator<Vector, Matrix>;
using NodeId = GraphBase::NodeId;
using EdgeId = GraphBase::EdgeId;
using NodeMetadata = RegAlloc::NodeMetadata;
struct EdgeMetadata {};
using GraphMetadata = RegAlloc::GraphMetadata;
using Graph = PBQP::Graph<RegAllocSolverImpl>;
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) {
assert(G.getNodeCosts(NId).getLength() > 1 &&
"PBQP Graph should not contain single or zero-option nodes");
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 handleDisconnectEdge(EdgeId EId, NodeId NId) {
NodeMetadata& NMd = G.getNodeMetadata(NId);
const MatrixMetadata& MMd = G.getEdgeCosts(EId).getMetadata();
NMd.handleRemoveEdge(MMd, NId == G.getEdgeNode2Id(EId));
promote(NId, NMd);
}
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 handleUpdateCosts(EdgeId EId, const Matrix& NewCosts) {
NodeId N1Id = G.getEdgeNode1Id(EId);
NodeId N2Id = G.getEdgeNode2Id(EId);
NodeMetadata& N1Md = G.getNodeMetadata(N1Id);
NodeMetadata& N2Md = G.getNodeMetadata(N2Id);
bool Transpose = N1Id != G.getEdgeNode1Id(EId);
// Metadata are computed incrementally. First, update them
// by removing the old cost.
const MatrixMetadata& OldMMd = G.getEdgeCosts(EId).getMetadata();
N1Md.handleRemoveEdge(OldMMd, Transpose);
N2Md.handleRemoveEdge(OldMMd, !Transpose);
// And update now the metadata with the new cost.
const MatrixMetadata& MMd = NewCosts.getMetadata();
N1Md.handleAddEdge(MMd, Transpose);
N2Md.handleAddEdge(MMd, !Transpose);
// As the metadata may have changed with the update, the nodes may have
// become ConservativelyAllocatable or OptimallyReducible.
promote(N1Id, N1Md);
promote(N2Id, N2Md);
}
private:
void promote(NodeId NId, NodeMetadata& NMd) {
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 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.");
using NodeId = GraphBase::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];
PBQPNum N2SC = G.getNodeCosts(N2Id)[0];
if (N1SC == N2SC)
return G.getNodeDegree(N1Id) < G.getNodeDegree(N2Id);
return N1SC < N2SC;
}
private:
const Graph& G;
};
Graph& G;
using NodeSet = std::set<NodeId>;
NodeSet OptimallyReducibleNodes;
NodeSet ConservativelyAllocatableNodes;
NodeSet NotProvablyAllocatableNodes;
};
class PBQPRAGraph : public PBQP::Graph<RegAllocSolverImpl> {
private:
using BaseT = PBQP::Graph<RegAllocSolverImpl>;
public:
PBQPRAGraph(GraphMetadata Metadata) : BaseT(std::move(Metadata)) {}
/// Dump this graph to dbgs().
void dump() const;
/// Dump this graph to an output stream.
/// @param OS Output stream to print on.
void dump(raw_ostream &OS) const;
/// Print a representation of this graph in DOT format.
/// @param OS Output stream to print on.
void printDot(raw_ostream &OS) const;
};
inline Solution solve(PBQPRAGraph& G) {
if (G.empty())
return Solution();
RegAllocSolverImpl RegAllocSolver(G);
return RegAllocSolver.solve();
}
} // end namespace RegAlloc
} // end namespace PBQP
/// Create a PBQP register allocator instance.
FunctionPass *
createPBQPRegisterAllocator(char *customPassID = nullptr);
} // end namespace llvm
#endif // LLVM_CODEGEN_REGALLOCPBQP_H