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llvm-project/llvm/lib/CodeGen/RegAllocPBQP.cpp

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//===- RegAllocPBQP.cpp ---- PBQP Register Allocator ----------------------===//
//
// 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 contains a Partitioned Boolean Quadratic Programming (PBQP) based
// register allocator for LLVM. This allocator works by constructing a PBQP
// problem representing the register allocation problem under consideration,
// solving this using a PBQP solver, and mapping the solution back to a
// register assignment. If any variables are selected for spilling then spill
// code is inserted and the process repeated.
//
// The PBQP solver (pbqp.c) provided for this allocator uses a heuristic tuned
// for register allocation. For more information on PBQP for register
// allocation, see the following papers:
//
// (1) Hames, L. and Scholz, B. 2006. Nearly optimal register allocation with
// PBQP. In Proceedings of the 7th Joint Modular Languages Conference
// (JMLC'06). LNCS, vol. 4228. Springer, New York, NY, USA. 346-361.
//
// (2) Scholz, B., Eckstein, E. 2002. Register allocation for irregular
// architectures. In Proceedings of the Joint Conference on Languages,
// Compilers and Tools for Embedded Systems (LCTES'02), ACM Press, New York,
// NY, USA, 139-148.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/RegAllocPBQP.h"
#include "RegisterCoalescer.h"
#include "Spiller.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/CodeGen/CalcSpillWeights.h"
#include "llvm/CodeGen/LiveInterval.h"
#include "llvm/CodeGen/LiveIntervals.h"
#include "llvm/CodeGen/LiveRangeEdit.h"
#include "llvm/CodeGen/LiveStacks.h"
#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/PBQP/Graph.h"
#include "llvm/CodeGen/PBQP/Math.h"
#include "llvm/CodeGen/PBQP/Solution.h"
#include "llvm/CodeGen/PBQPRAConstraint.h"
#include "llvm/CodeGen/RegAllocRegistry.h"
#include "llvm/CodeGen/SlotIndexes.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/CodeGen/VirtRegMap.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Module.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/Printable.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <limits>
#include <map>
#include <memory>
#include <queue>
#include <set>
#include <sstream>
#include <string>
#include <system_error>
#include <tuple>
#include <utility>
#include <vector>
using namespace llvm;
#define DEBUG_TYPE "regalloc"
static RegisterRegAlloc
RegisterPBQPRepAlloc("pbqp", "PBQP register allocator",
createDefaultPBQPRegisterAllocator);
static cl::opt<bool>
PBQPCoalescing("pbqp-coalescing",
cl::desc("Attempt coalescing during PBQP register allocation."),
cl::init(false), cl::Hidden);
#ifndef NDEBUG
static cl::opt<bool>
PBQPDumpGraphs("pbqp-dump-graphs",
cl::desc("Dump graphs for each function/round in the compilation unit."),
cl::init(false), cl::Hidden);
#endif
namespace {
///
/// PBQP based allocators solve the register allocation problem by mapping
/// register allocation problems to Partitioned Boolean Quadratic
/// Programming problems.
class RegAllocPBQP : public MachineFunctionPass {
public:
static char ID;
/// Construct a PBQP register allocator.
RegAllocPBQP(char *cPassID = nullptr)
: MachineFunctionPass(ID), customPassID(cPassID) {
initializeSlotIndexesPass(*PassRegistry::getPassRegistry());
initializeLiveIntervalsPass(*PassRegistry::getPassRegistry());
initializeLiveStacksPass(*PassRegistry::getPassRegistry());
initializeVirtRegMapPass(*PassRegistry::getPassRegistry());
}
/// Return the pass name.
StringRef getPassName() const override { return "PBQP Register Allocator"; }
/// PBQP analysis usage.
void getAnalysisUsage(AnalysisUsage &au) const override;
/// Perform register allocation
bool runOnMachineFunction(MachineFunction &MF) override;
MachineFunctionProperties getRequiredProperties() const override {
return MachineFunctionProperties().set(
MachineFunctionProperties::Property::NoPHIs);
}
private:
using LI2NodeMap = std::map<const LiveInterval *, unsigned>;
using Node2LIMap = std::vector<const LiveInterval *>;
using AllowedSet = std::vector<unsigned>;
using AllowedSetMap = std::vector<AllowedSet>;
using RegPair = std::pair<unsigned, unsigned>;
using CoalesceMap = std::map<RegPair, PBQP::PBQPNum>;
using RegSet = std::set<unsigned>;
char *customPassID;
RegSet VRegsToAlloc, EmptyIntervalVRegs;
/// Inst which is a def of an original reg and whose defs are already all
/// dead after remat is saved in DeadRemats. The deletion of such inst is
/// postponed till all the allocations are done, so its remat expr is
/// always available for the remat of all the siblings of the original reg.
SmallPtrSet<MachineInstr *, 32> DeadRemats;
/// Finds the initial set of vreg intervals to allocate.
void findVRegIntervalsToAlloc(const MachineFunction &MF, LiveIntervals &LIS);
/// Constructs an initial graph.
void initializeGraph(PBQPRAGraph &G, VirtRegMap &VRM, Spiller &VRegSpiller);
/// Spill the given VReg.
void spillVReg(unsigned VReg, SmallVectorImpl<unsigned> &NewIntervals,
MachineFunction &MF, LiveIntervals &LIS, VirtRegMap &VRM,
Spiller &VRegSpiller);
/// Given a solved PBQP problem maps this solution back to a register
/// assignment.
bool mapPBQPToRegAlloc(const PBQPRAGraph &G,
const PBQP::Solution &Solution,
VirtRegMap &VRM,
Spiller &VRegSpiller);
/// Postprocessing before final spilling. Sets basic block "live in"
/// variables.
void finalizeAlloc(MachineFunction &MF, LiveIntervals &LIS,
VirtRegMap &VRM) const;
void postOptimization(Spiller &VRegSpiller, LiveIntervals &LIS);
};
char RegAllocPBQP::ID = 0;
/// Set spill costs for each node in the PBQP reg-alloc graph.
class SpillCosts : public PBQPRAConstraint {
public:
void apply(PBQPRAGraph &G) override {
LiveIntervals &LIS = G.getMetadata().LIS;
// A minimum spill costs, so that register constraints can can be set
// without normalization in the [0.0:MinSpillCost( interval.
const PBQP::PBQPNum MinSpillCost = 10.0;
for (auto NId : G.nodeIds()) {
PBQP::PBQPNum SpillCost =
LIS.getInterval(G.getNodeMetadata(NId).getVReg()).weight;
if (SpillCost == 0.0)
SpillCost = std::numeric_limits<PBQP::PBQPNum>::min();
else
SpillCost += MinSpillCost;
PBQPRAGraph::RawVector NodeCosts(G.getNodeCosts(NId));
NodeCosts[PBQP::RegAlloc::getSpillOptionIdx()] = SpillCost;
G.setNodeCosts(NId, std::move(NodeCosts));
}
}
};
/// Add interference edges between overlapping vregs.
class Interference : public PBQPRAConstraint {
private:
using AllowedRegVecPtr = const PBQP::RegAlloc::AllowedRegVector *;
using IKey = std::pair<AllowedRegVecPtr, AllowedRegVecPtr>;
using IMatrixCache = DenseMap<IKey, PBQPRAGraph::MatrixPtr>;
using DisjointAllowedRegsCache = DenseSet<IKey>;
using IEdgeKey = std::pair<PBQP::GraphBase::NodeId, PBQP::GraphBase::NodeId>;
using IEdgeCache = DenseSet<IEdgeKey>;
bool haveDisjointAllowedRegs(const PBQPRAGraph &G, PBQPRAGraph::NodeId NId,
PBQPRAGraph::NodeId MId,
const DisjointAllowedRegsCache &D) const {
const auto *NRegs = &G.getNodeMetadata(NId).getAllowedRegs();
const auto *MRegs = &G.getNodeMetadata(MId).getAllowedRegs();
if (NRegs == MRegs)
return false;
if (NRegs < MRegs)
return D.count(IKey(NRegs, MRegs)) > 0;
return D.count(IKey(MRegs, NRegs)) > 0;
}
void setDisjointAllowedRegs(const PBQPRAGraph &G, PBQPRAGraph::NodeId NId,
PBQPRAGraph::NodeId MId,
DisjointAllowedRegsCache &D) {
const auto *NRegs = &G.getNodeMetadata(NId).getAllowedRegs();
const auto *MRegs = &G.getNodeMetadata(MId).getAllowedRegs();
assert(NRegs != MRegs && "AllowedRegs can not be disjoint with itself");
if (NRegs < MRegs)
D.insert(IKey(NRegs, MRegs));
else
D.insert(IKey(MRegs, NRegs));
}
// Holds (Interval, CurrentSegmentID, and NodeId). The first two are required
// for the fast interference graph construction algorithm. The last is there
// to save us from looking up node ids via the VRegToNode map in the graph
// metadata.
using IntervalInfo =
std::tuple<LiveInterval*, size_t, PBQP::GraphBase::NodeId>;
static SlotIndex getStartPoint(const IntervalInfo &I) {
return std::get<0>(I)->segments[std::get<1>(I)].start;
}
static SlotIndex getEndPoint(const IntervalInfo &I) {
return std::get<0>(I)->segments[std::get<1>(I)].end;
}
static PBQP::GraphBase::NodeId getNodeId(const IntervalInfo &I) {
return std::get<2>(I);
}
static bool lowestStartPoint(const IntervalInfo &I1,
const IntervalInfo &I2) {
// Condition reversed because priority queue has the *highest* element at
// the front, rather than the lowest.
return getStartPoint(I1) > getStartPoint(I2);
}
static bool lowestEndPoint(const IntervalInfo &I1,
const IntervalInfo &I2) {
SlotIndex E1 = getEndPoint(I1);
SlotIndex E2 = getEndPoint(I2);
if (E1 < E2)
return true;
if (E1 > E2)
return false;
// If two intervals end at the same point, we need a way to break the tie or
// the set will assume they're actually equal and refuse to insert a
// "duplicate". Just compare the vregs - fast and guaranteed unique.
return std::get<0>(I1)->reg < std::get<0>(I2)->reg;
}
static bool isAtLastSegment(const IntervalInfo &I) {
return std::get<1>(I) == std::get<0>(I)->size() - 1;
}
static IntervalInfo nextSegment(const IntervalInfo &I) {
return std::make_tuple(std::get<0>(I), std::get<1>(I) + 1, std::get<2>(I));
}
public:
void apply(PBQPRAGraph &G) override {
// The following is loosely based on the linear scan algorithm introduced in
// "Linear Scan Register Allocation" by Poletto and Sarkar. This version
// isn't linear, because the size of the active set isn't bound by the
// number of registers, but rather the size of the largest clique in the
// graph. Still, we expect this to be better than N^2.
LiveIntervals &LIS = G.getMetadata().LIS;
// Interferenc matrices are incredibly regular - they're only a function of
// the allowed sets, so we cache them to avoid the overhead of constructing
// and uniquing them.
IMatrixCache C;
// Finding an edge is expensive in the worst case (O(max_clique(G))). So
// cache locally edges we have already seen.
IEdgeCache EC;
// Cache known disjoint allowed registers pairs
DisjointAllowedRegsCache D;
using IntervalSet = std::set<IntervalInfo, decltype(&lowestEndPoint)>;
using IntervalQueue =
std::priority_queue<IntervalInfo, std::vector<IntervalInfo>,
decltype(&lowestStartPoint)>;
IntervalSet Active(lowestEndPoint);
IntervalQueue Inactive(lowestStartPoint);
// Start by building the inactive set.
for (auto NId : G.nodeIds()) {
unsigned VReg = G.getNodeMetadata(NId).getVReg();
LiveInterval &LI = LIS.getInterval(VReg);
assert(!LI.empty() && "PBQP graph contains node for empty interval");
Inactive.push(std::make_tuple(&LI, 0, NId));
}
while (!Inactive.empty()) {
// Tentatively grab the "next" interval - this choice may be overriden
// below.
IntervalInfo Cur = Inactive.top();
// Retire any active intervals that end before Cur starts.
IntervalSet::iterator RetireItr = Active.begin();
while (RetireItr != Active.end() &&
(getEndPoint(*RetireItr) <= getStartPoint(Cur))) {
// If this interval has subsequent segments, add the next one to the
// inactive list.
if (!isAtLastSegment(*RetireItr))
Inactive.push(nextSegment(*RetireItr));
++RetireItr;
}
Active.erase(Active.begin(), RetireItr);
// One of the newly retired segments may actually start before the
// Cur segment, so re-grab the front of the inactive list.
Cur = Inactive.top();
Inactive.pop();
// At this point we know that Cur overlaps all active intervals. Add the
// interference edges.
PBQP::GraphBase::NodeId NId = getNodeId(Cur);
for (const auto &A : Active) {
PBQP::GraphBase::NodeId MId = getNodeId(A);
// Do not add an edge when the nodes' allowed registers do not
// intersect: there is obviously no interference.
if (haveDisjointAllowedRegs(G, NId, MId, D))
continue;
// Check that we haven't already added this edge
IEdgeKey EK(std::min(NId, MId), std::max(NId, MId));
if (EC.count(EK))
continue;
// This is a new edge - add it to the graph.
if (!createInterferenceEdge(G, NId, MId, C))
setDisjointAllowedRegs(G, NId, MId, D);
else
EC.insert(EK);
}
// Finally, add Cur to the Active set.
Active.insert(Cur);
}
}
private:
// Create an Interference edge and add it to the graph, unless it is
// a null matrix, meaning the nodes' allowed registers do not have any
// interference. This case occurs frequently between integer and floating
// point registers for example.
// return true iff both nodes interferes.
bool createInterferenceEdge(PBQPRAGraph &G,
PBQPRAGraph::NodeId NId, PBQPRAGraph::NodeId MId,
IMatrixCache &C) {
const TargetRegisterInfo &TRI =
*G.getMetadata().MF.getSubtarget().getRegisterInfo();
const auto &NRegs = G.getNodeMetadata(NId).getAllowedRegs();
const auto &MRegs = G.getNodeMetadata(MId).getAllowedRegs();
// Try looking the edge costs up in the IMatrixCache first.
IKey K(&NRegs, &MRegs);
IMatrixCache::iterator I = C.find(K);
if (I != C.end()) {
G.addEdgeBypassingCostAllocator(NId, MId, I->second);
return true;
}
PBQPRAGraph::RawMatrix M(NRegs.size() + 1, MRegs.size() + 1, 0);
bool NodesInterfere = false;
for (unsigned I = 0; I != NRegs.size(); ++I) {
unsigned PRegN = NRegs[I];
for (unsigned J = 0; J != MRegs.size(); ++J) {
unsigned PRegM = MRegs[J];
if (TRI.regsOverlap(PRegN, PRegM)) {
M[I + 1][J + 1] = std::numeric_limits<PBQP::PBQPNum>::infinity();
NodesInterfere = true;
}
}
}
if (!NodesInterfere)
return false;
PBQPRAGraph::EdgeId EId = G.addEdge(NId, MId, std::move(M));
C[K] = G.getEdgeCostsPtr(EId);
return true;
}
};
class Coalescing : public PBQPRAConstraint {
public:
void apply(PBQPRAGraph &G) override {
MachineFunction &MF = G.getMetadata().MF;
MachineBlockFrequencyInfo &MBFI = G.getMetadata().MBFI;
CoalescerPair CP(*MF.getSubtarget().getRegisterInfo());
// Scan the machine function and add a coalescing cost whenever CoalescerPair
// gives the Ok.
for (const auto &MBB : MF) {
for (const auto &MI : MBB) {
// Skip not-coalescable or already coalesced copies.
if (!CP.setRegisters(&MI) || CP.getSrcReg() == CP.getDstReg())
continue;
unsigned DstReg = CP.getDstReg();
unsigned SrcReg = CP.getSrcReg();
const float Scale = 1.0f / MBFI.getEntryFreq();
PBQP::PBQPNum CBenefit = MBFI.getBlockFreq(&MBB).getFrequency() * Scale;
if (CP.isPhys()) {
if (!MF.getRegInfo().isAllocatable(DstReg))
continue;
PBQPRAGraph::NodeId NId = G.getMetadata().getNodeIdForVReg(SrcReg);
const PBQPRAGraph::NodeMetadata::AllowedRegVector &Allowed =
G.getNodeMetadata(NId).getAllowedRegs();
unsigned PRegOpt = 0;
while (PRegOpt < Allowed.size() && Allowed[PRegOpt] != DstReg)
++PRegOpt;
if (PRegOpt < Allowed.size()) {
PBQPRAGraph::RawVector NewCosts(G.getNodeCosts(NId));
NewCosts[PRegOpt + 1] -= CBenefit;
G.setNodeCosts(NId, std::move(NewCosts));
}
} else {
PBQPRAGraph::NodeId N1Id = G.getMetadata().getNodeIdForVReg(DstReg);
PBQPRAGraph::NodeId N2Id = G.getMetadata().getNodeIdForVReg(SrcReg);
const PBQPRAGraph::NodeMetadata::AllowedRegVector *Allowed1 =
&G.getNodeMetadata(N1Id).getAllowedRegs();
const PBQPRAGraph::NodeMetadata::AllowedRegVector *Allowed2 =
&G.getNodeMetadata(N2Id).getAllowedRegs();
PBQPRAGraph::EdgeId EId = G.findEdge(N1Id, N2Id);
if (EId == G.invalidEdgeId()) {
PBQPRAGraph::RawMatrix Costs(Allowed1->size() + 1,
Allowed2->size() + 1, 0);
addVirtRegCoalesce(Costs, *Allowed1, *Allowed2, CBenefit);
G.addEdge(N1Id, N2Id, std::move(Costs));
} else {
if (G.getEdgeNode1Id(EId) == N2Id) {
std::swap(N1Id, N2Id);
std::swap(Allowed1, Allowed2);
}
PBQPRAGraph::RawMatrix Costs(G.getEdgeCosts(EId));
addVirtRegCoalesce(Costs, *Allowed1, *Allowed2, CBenefit);
G.updateEdgeCosts(EId, std::move(Costs));
}
}
}
}
}
private:
void addVirtRegCoalesce(
PBQPRAGraph::RawMatrix &CostMat,
const PBQPRAGraph::NodeMetadata::AllowedRegVector &Allowed1,
const PBQPRAGraph::NodeMetadata::AllowedRegVector &Allowed2,
PBQP::PBQPNum Benefit) {
assert(CostMat.getRows() == Allowed1.size() + 1 && "Size mismatch.");
assert(CostMat.getCols() == Allowed2.size() + 1 && "Size mismatch.");
for (unsigned I = 0; I != Allowed1.size(); ++I) {
unsigned PReg1 = Allowed1[I];
for (unsigned J = 0; J != Allowed2.size(); ++J) {
unsigned PReg2 = Allowed2[J];
if (PReg1 == PReg2)
CostMat[I + 1][J + 1] -= Benefit;
}
}
}
};
} // end anonymous namespace
// Out-of-line destructor/anchor for PBQPRAConstraint.
PBQPRAConstraint::~PBQPRAConstraint() = default;
void PBQPRAConstraint::anchor() {}
void PBQPRAConstraintList::anchor() {}
void RegAllocPBQP::getAnalysisUsage(AnalysisUsage &au) const {
au.setPreservesCFG();
au.addRequired<AAResultsWrapperPass>();
au.addPreserved<AAResultsWrapperPass>();
au.addRequired<SlotIndexes>();
au.addPreserved<SlotIndexes>();
au.addRequired<LiveIntervals>();
au.addPreserved<LiveIntervals>();
//au.addRequiredID(SplitCriticalEdgesID);
if (customPassID)
au.addRequiredID(*customPassID);
au.addRequired<LiveStacks>();
au.addPreserved<LiveStacks>();
au.addRequired<MachineBlockFrequencyInfo>();
au.addPreserved<MachineBlockFrequencyInfo>();
au.addRequired<MachineLoopInfo>();
au.addPreserved<MachineLoopInfo>();
au.addRequired<MachineDominatorTree>();
au.addPreserved<MachineDominatorTree>();
au.addRequired<VirtRegMap>();
au.addPreserved<VirtRegMap>();
MachineFunctionPass::getAnalysisUsage(au);
}
void RegAllocPBQP::findVRegIntervalsToAlloc(const MachineFunction &MF,
LiveIntervals &LIS) {
const MachineRegisterInfo &MRI = MF.getRegInfo();
// Iterate over all live ranges.
for (unsigned I = 0, E = MRI.getNumVirtRegs(); I != E; ++I) {
unsigned Reg = TargetRegisterInfo::index2VirtReg(I);
if (MRI.reg_nodbg_empty(Reg))
continue;
VRegsToAlloc.insert(Reg);
}
}
static bool isACalleeSavedRegister(unsigned reg, const TargetRegisterInfo &TRI,
const MachineFunction &MF) {
const MCPhysReg *CSR = MF.getRegInfo().getCalleeSavedRegs();
for (unsigned i = 0; CSR[i] != 0; ++i)
if (TRI.regsOverlap(reg, CSR[i]))
return true;
return false;
}
void RegAllocPBQP::initializeGraph(PBQPRAGraph &G, VirtRegMap &VRM,
Spiller &VRegSpiller) {
MachineFunction &MF = G.getMetadata().MF;
LiveIntervals &LIS = G.getMetadata().LIS;
const MachineRegisterInfo &MRI = G.getMetadata().MF.getRegInfo();
const TargetRegisterInfo &TRI =
*G.getMetadata().MF.getSubtarget().getRegisterInfo();
std::vector<unsigned> Worklist(VRegsToAlloc.begin(), VRegsToAlloc.end());
std::map<unsigned, std::vector<unsigned>> VRegAllowedMap;
while (!Worklist.empty()) {
unsigned VReg = Worklist.back();
Worklist.pop_back();
LiveInterval &VRegLI = LIS.getInterval(VReg);
// If this is an empty interval move it to the EmptyIntervalVRegs set then
// continue.
if (VRegLI.empty()) {
EmptyIntervalVRegs.insert(VRegLI.reg);
VRegsToAlloc.erase(VRegLI.reg);
continue;
}
const TargetRegisterClass *TRC = MRI.getRegClass(VReg);
// Record any overlaps with regmask operands.
BitVector RegMaskOverlaps;
LIS.checkRegMaskInterference(VRegLI, RegMaskOverlaps);
// Compute an initial allowed set for the current vreg.
std::vector<unsigned> VRegAllowed;
ArrayRef<MCPhysReg> RawPRegOrder = TRC->getRawAllocationOrder(MF);
for (unsigned I = 0; I != RawPRegOrder.size(); ++I) {
unsigned PReg = RawPRegOrder[I];
if (MRI.isReserved(PReg))
continue;
// vregLI crosses a regmask operand that clobbers preg.
if (!RegMaskOverlaps.empty() && !RegMaskOverlaps.test(PReg))
continue;
// vregLI overlaps fixed regunit interference.
bool Interference = false;
for (MCRegUnitIterator Units(PReg, &TRI); Units.isValid(); ++Units) {
if (VRegLI.overlaps(LIS.getRegUnit(*Units))) {
Interference = true;
break;
}
}
if (Interference)
continue;
// preg is usable for this virtual register.
VRegAllowed.push_back(PReg);
}
// Check for vregs that have no allowed registers. These should be
// pre-spilled and the new vregs added to the worklist.
if (VRegAllowed.empty()) {
SmallVector<unsigned, 8> NewVRegs;
spillVReg(VReg, NewVRegs, MF, LIS, VRM, VRegSpiller);
Worklist.insert(Worklist.end(), NewVRegs.begin(), NewVRegs.end());
continue;
} else
VRegAllowedMap[VReg] = std::move(VRegAllowed);
}
for (auto &KV : VRegAllowedMap) {
auto VReg = KV.first;
// Move empty intervals to the EmptyIntervalVReg set.
if (LIS.getInterval(VReg).empty()) {
EmptyIntervalVRegs.insert(VReg);
VRegsToAlloc.erase(VReg);
continue;
}
auto &VRegAllowed = KV.second;
PBQPRAGraph::RawVector NodeCosts(VRegAllowed.size() + 1, 0);
// Tweak cost of callee saved registers, as using then force spilling and
// restoring them. This would only happen in the prologue / epilogue though.
for (unsigned i = 0; i != VRegAllowed.size(); ++i)
if (isACalleeSavedRegister(VRegAllowed[i], TRI, MF))
NodeCosts[1 + i] += 1.0;
PBQPRAGraph::NodeId NId = G.addNode(std::move(NodeCosts));
G.getNodeMetadata(NId).setVReg(VReg);
G.getNodeMetadata(NId).setAllowedRegs(
G.getMetadata().getAllowedRegs(std::move(VRegAllowed)));
G.getMetadata().setNodeIdForVReg(VReg, NId);
}
}
void RegAllocPBQP::spillVReg(unsigned VReg,
SmallVectorImpl<unsigned> &NewIntervals,
MachineFunction &MF, LiveIntervals &LIS,
VirtRegMap &VRM, Spiller &VRegSpiller) {
VRegsToAlloc.erase(VReg);
LiveRangeEdit LRE(&LIS.getInterval(VReg), NewIntervals, MF, LIS, &VRM,
nullptr, &DeadRemats);
VRegSpiller.spill(LRE);
const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
(void)TRI;
LLVM_DEBUG(dbgs() << "VREG " << printReg(VReg, &TRI) << " -> SPILLED (Cost: "
<< LRE.getParent().weight << ", New vregs: ");
// Copy any newly inserted live intervals into the list of regs to
// allocate.
for (LiveRangeEdit::iterator I = LRE.begin(), E = LRE.end();
I != E; ++I) {
const LiveInterval &LI = LIS.getInterval(*I);
assert(!LI.empty() && "Empty spill range.");
LLVM_DEBUG(dbgs() << printReg(LI.reg, &TRI) << " ");
VRegsToAlloc.insert(LI.reg);
}
LLVM_DEBUG(dbgs() << ")\n");
}
bool RegAllocPBQP::mapPBQPToRegAlloc(const PBQPRAGraph &G,
const PBQP::Solution &Solution,
VirtRegMap &VRM,
Spiller &VRegSpiller) {
MachineFunction &MF = G.getMetadata().MF;
LiveIntervals &LIS = G.getMetadata().LIS;
const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
(void)TRI;
// Set to true if we have any spills
bool AnotherRoundNeeded = false;
// Clear the existing allocation.
VRM.clearAllVirt();
// Iterate over the nodes mapping the PBQP solution to a register
// assignment.
for (auto NId : G.nodeIds()) {
unsigned VReg = G.getNodeMetadata(NId).getVReg();
unsigned AllocOption = Solution.getSelection(NId);
if (AllocOption != PBQP::RegAlloc::getSpillOptionIdx()) {
unsigned PReg = G.getNodeMetadata(NId).getAllowedRegs()[AllocOption - 1];
LLVM_DEBUG(dbgs() << "VREG " << printReg(VReg, &TRI) << " -> "
<< TRI.getName(PReg) << "\n");
assert(PReg != 0 && "Invalid preg selected.");
VRM.assignVirt2Phys(VReg, PReg);
} else {
// Spill VReg. If this introduces new intervals we'll need another round
// of allocation.
SmallVector<unsigned, 8> NewVRegs;
spillVReg(VReg, NewVRegs, MF, LIS, VRM, VRegSpiller);
AnotherRoundNeeded |= !NewVRegs.empty();
}
}
return !AnotherRoundNeeded;
}
void RegAllocPBQP::finalizeAlloc(MachineFunction &MF,
LiveIntervals &LIS,
VirtRegMap &VRM) const {
MachineRegisterInfo &MRI = MF.getRegInfo();
// First allocate registers for the empty intervals.
for (RegSet::const_iterator
I = EmptyIntervalVRegs.begin(), E = EmptyIntervalVRegs.end();
I != E; ++I) {
LiveInterval &LI = LIS.getInterval(*I);
unsigned PReg = MRI.getSimpleHint(LI.reg);
if (PReg == 0) {
const TargetRegisterClass &RC = *MRI.getRegClass(LI.reg);
const ArrayRef<MCPhysReg> RawPRegOrder = RC.getRawAllocationOrder(MF);
for (unsigned CandidateReg : RawPRegOrder) {
if (!VRM.getRegInfo().isReserved(CandidateReg)) {
PReg = CandidateReg;
break;
}
}
assert(PReg &&
"No un-reserved physical registers in this register class");
}
VRM.assignVirt2Phys(LI.reg, PReg);
}
}
void RegAllocPBQP::postOptimization(Spiller &VRegSpiller, LiveIntervals &LIS) {
VRegSpiller.postOptimization();
/// Remove dead defs because of rematerialization.
for (auto DeadInst : DeadRemats) {
LIS.RemoveMachineInstrFromMaps(*DeadInst);
DeadInst->eraseFromParent();
}
DeadRemats.clear();
}
static inline float normalizePBQPSpillWeight(float UseDefFreq, unsigned Size,
unsigned NumInstr) {
// All intervals have a spill weight that is mostly proportional to the number
// of uses, with uses in loops having a bigger weight.
return NumInstr * normalizeSpillWeight(UseDefFreq, Size, 1);
}
bool RegAllocPBQP::runOnMachineFunction(MachineFunction &MF) {
LiveIntervals &LIS = getAnalysis<LiveIntervals>();
MachineBlockFrequencyInfo &MBFI =
getAnalysis<MachineBlockFrequencyInfo>();
VirtRegMap &VRM = getAnalysis<VirtRegMap>();
calculateSpillWeightsAndHints(LIS, MF, &VRM, getAnalysis<MachineLoopInfo>(),
MBFI, normalizePBQPSpillWeight);
std::unique_ptr<Spiller> VRegSpiller(createInlineSpiller(*this, MF, VRM));
MF.getRegInfo().freezeReservedRegs(MF);
LLVM_DEBUG(dbgs() << "PBQP Register Allocating for " << MF.getName() << "\n");
// Allocator main loop:
//
// * Map current regalloc problem to a PBQP problem
// * Solve the PBQP problem
// * Map the solution back to a register allocation
// * Spill if necessary
//
// This process is continued till no more spills are generated.
// Find the vreg intervals in need of allocation.
findVRegIntervalsToAlloc(MF, LIS);
#ifndef NDEBUG
const Function &F = MF.getFunction();
std::string FullyQualifiedName =
F.getParent()->getModuleIdentifier() + "." + F.getName().str();
#endif
// If there are non-empty intervals allocate them using pbqp.
if (!VRegsToAlloc.empty()) {
const TargetSubtargetInfo &Subtarget = MF.getSubtarget();
std::unique_ptr<PBQPRAConstraintList> ConstraintsRoot =
llvm::make_unique<PBQPRAConstraintList>();
ConstraintsRoot->addConstraint(llvm::make_unique<SpillCosts>());
ConstraintsRoot->addConstraint(llvm::make_unique<Interference>());
if (PBQPCoalescing)
ConstraintsRoot->addConstraint(llvm::make_unique<Coalescing>());
ConstraintsRoot->addConstraint(Subtarget.getCustomPBQPConstraints());
bool PBQPAllocComplete = false;
unsigned Round = 0;
while (!PBQPAllocComplete) {
LLVM_DEBUG(dbgs() << " PBQP Regalloc round " << Round << ":\n");
PBQPRAGraph G(PBQPRAGraph::GraphMetadata(MF, LIS, MBFI));
initializeGraph(G, VRM, *VRegSpiller);
ConstraintsRoot->apply(G);
#ifndef NDEBUG
if (PBQPDumpGraphs) {
std::ostringstream RS;
RS << Round;
std::string GraphFileName = FullyQualifiedName + "." + RS.str() +
".pbqpgraph";
std::error_code EC;
raw_fd_ostream OS(GraphFileName, EC, sys::fs::F_Text);
LLVM_DEBUG(dbgs() << "Dumping graph for round " << Round << " to \""
<< GraphFileName << "\"\n");
G.dump(OS);
}
#endif
PBQP::Solution Solution = PBQP::RegAlloc::solve(G);
PBQPAllocComplete = mapPBQPToRegAlloc(G, Solution, VRM, *VRegSpiller);
++Round;
}
}
// Finalise allocation, allocate empty ranges.
finalizeAlloc(MF, LIS, VRM);
postOptimization(*VRegSpiller, LIS);
VRegsToAlloc.clear();
EmptyIntervalVRegs.clear();
LLVM_DEBUG(dbgs() << "Post alloc VirtRegMap:\n" << VRM << "\n");
return true;
}
/// Create Printable object for node and register info.
static Printable PrintNodeInfo(PBQP::RegAlloc::PBQPRAGraph::NodeId NId,
const PBQP::RegAlloc::PBQPRAGraph &G) {
return Printable([NId, &G](raw_ostream &OS) {
const MachineRegisterInfo &MRI = G.getMetadata().MF.getRegInfo();
const TargetRegisterInfo *TRI = MRI.getTargetRegisterInfo();
unsigned VReg = G.getNodeMetadata(NId).getVReg();
const char *RegClassName = TRI->getRegClassName(MRI.getRegClass(VReg));
OS << NId << " (" << RegClassName << ':' << printReg(VReg, TRI) << ')';
});
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void PBQP::RegAlloc::PBQPRAGraph::dump(raw_ostream &OS) const {
for (auto NId : nodeIds()) {
const Vector &Costs = getNodeCosts(NId);
assert(Costs.getLength() != 0 && "Empty vector in graph.");
OS << PrintNodeInfo(NId, *this) << ": " << Costs << '\n';
}
OS << '\n';
for (auto EId : edgeIds()) {
NodeId N1Id = getEdgeNode1Id(EId);
NodeId N2Id = getEdgeNode2Id(EId);
assert(N1Id != N2Id && "PBQP graphs should not have self-edges.");
const Matrix &M = getEdgeCosts(EId);
assert(M.getRows() != 0 && "No rows in matrix.");
assert(M.getCols() != 0 && "No cols in matrix.");
OS << PrintNodeInfo(N1Id, *this) << ' ' << M.getRows() << " rows / ";
OS << PrintNodeInfo(N2Id, *this) << ' ' << M.getCols() << " cols:\n";
OS << M << '\n';
}
}
LLVM_DUMP_METHOD void PBQP::RegAlloc::PBQPRAGraph::dump() const {
dump(dbgs());
}
#endif
void PBQP::RegAlloc::PBQPRAGraph::printDot(raw_ostream &OS) const {
OS << "graph {\n";
for (auto NId : nodeIds()) {
OS << " node" << NId << " [ label=\""
<< PrintNodeInfo(NId, *this) << "\\n"
<< getNodeCosts(NId) << "\" ]\n";
}
OS << " edge [ len=" << nodeIds().size() << " ]\n";
for (auto EId : edgeIds()) {
OS << " node" << getEdgeNode1Id(EId)
<< " -- node" << getEdgeNode2Id(EId)
<< " [ label=\"";
const Matrix &EdgeCosts = getEdgeCosts(EId);
for (unsigned i = 0; i < EdgeCosts.getRows(); ++i) {
OS << EdgeCosts.getRowAsVector(i) << "\\n";
}
OS << "\" ]\n";
}
OS << "}\n";
}
FunctionPass *llvm::createPBQPRegisterAllocator(char *customPassID) {
return new RegAllocPBQP(customPassID);
}
FunctionPass* llvm::createDefaultPBQPRegisterAllocator() {
return createPBQPRegisterAllocator();
}
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