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llvm-mirror/lib/CodeGen/RegAllocPBQP.cpp
Chandler Carruth ae65e281f3 Update the file headers across all of the LLVM projects in the monorepo 
to reflect the new license.

We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.

Essentially, all code in the project is now made available by the LLVM
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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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