//===------ RegAllocPBQP.cpp ---- PBQP Register Allocator -------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// 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.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "regalloc"
#include "llvm/CodeGen/RegAllocPBQP.h"
#include "RegisterCoalescer.h"
#include "Spiller.h"
#include "llvm/ADT/OwningPtr.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/CodeGen/CalcSpillWeights.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/LiveRangeEdit.h"
#include "llvm/CodeGen/LiveStackAnalysis.h"
#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/PBQP/Graph.h"
#include "llvm/CodeGen/PBQP/HeuristicSolver.h"
#include "llvm/CodeGen/PBQP/Heuristics/Briggs.h"
#include "llvm/CodeGen/RegAllocRegistry.h"
#include "llvm/CodeGen/VirtRegMap.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include <limits>
#include <memory>
#include <set>
#include <sstream>
#include <vector>
using namespace llvm;
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(OwningPtr<PBQPBuilder> &b, char *cPassID=0)
: MachineFunctionPass(ID), builder(b.take()), customPassID(cPassID) {
initializeSlotIndexesPass(*PassRegistry::getPassRegistry());
initializeLiveIntervalsPass(*PassRegistry::getPassRegistry());
initializeCalculateSpillWeightsPass(*PassRegistry::getPassRegistry());
initializeLiveStacksPass(*PassRegistry::getPassRegistry());
initializeVirtRegMapPass(*PassRegistry::getPassRegistry());
}
/// Return the pass name.
virtual const char* getPassName() const {
return "PBQP Register Allocator";
}
/// PBQP analysis usage.
virtual void getAnalysisUsage(AnalysisUsage &au) const;
/// Perform register allocation
virtual bool runOnMachineFunction(MachineFunction &MF);
private:
typedef std::map<const LiveInterval*, unsigned> LI2NodeMap;
typedef std::vector<const LiveInterval*> Node2LIMap;
typedef std::vector<unsigned> AllowedSet;
typedef std::vector<AllowedSet> AllowedSetMap;
typedef std::pair<unsigned, unsigned> RegPair;
typedef std::map<RegPair, PBQP::PBQPNum> CoalesceMap;
typedef std::set<unsigned> RegSet;
OwningPtr<PBQPBuilder> builder;
char *customPassID;
MachineFunction *mf;
const TargetMachine *tm;
const TargetRegisterInfo *tri;
const TargetInstrInfo *tii;
MachineRegisterInfo *mri;
const MachineBlockFrequencyInfo *mbfi;
OwningPtr<Spiller> spiller;
LiveIntervals *lis;
LiveStacks *lss;
VirtRegMap *vrm;
RegSet vregsToAlloc, emptyIntervalVRegs;
/// \brief Finds the initial set of vreg intervals to allocate.
void findVRegIntervalsToAlloc();
/// \brief Given a solved PBQP problem maps this solution back to a register
/// assignment.
bool mapPBQPToRegAlloc(const PBQPRAProblem &problem,
const PBQP::Solution &solution);
/// \brief Postprocessing before final spilling. Sets basic block "live in"
/// variables.
void finalizeAlloc() const;
};
char RegAllocPBQP::ID = 0;
} // End anonymous namespace.
unsigned PBQPRAProblem::getVRegForNode(PBQP::Graph::ConstNodeItr node) const {
Node2VReg::const_iterator vregItr = node2VReg.find(node);
assert(vregItr != node2VReg.end() && "No vreg for node.");
return vregItr->second;
}
PBQP::Graph::NodeItr PBQPRAProblem::getNodeForVReg(unsigned vreg) const {
VReg2Node::const_iterator nodeItr = vreg2Node.find(vreg);
assert(nodeItr != vreg2Node.end() && "No node for vreg.");
return nodeItr->second;
}
const PBQPRAProblem::AllowedSet&
PBQPRAProblem::getAllowedSet(unsigned vreg) const {
AllowedSetMap::const_iterator allowedSetItr = allowedSets.find(vreg);
assert(allowedSetItr != allowedSets.end() && "No pregs for vreg.");
const AllowedSet &allowedSet = allowedSetItr->second;
return allowedSet;
}
unsigned PBQPRAProblem::getPRegForOption(unsigned vreg, unsigned option) const {
assert(isPRegOption(vreg, option) && "Not a preg option.");
const AllowedSet& allowedSet = getAllowedSet(vreg);
assert(option <= allowedSet.size() && "Option outside allowed set.");
return allowedSet[option - 1];
}
PBQPRAProblem *PBQPBuilder::build(MachineFunction *mf, const LiveIntervals *lis,
const MachineBlockFrequencyInfo *mbfi,
const RegSet &vregs) {
LiveIntervals *LIS = const_cast<LiveIntervals*>(lis);
MachineRegisterInfo *mri = &mf->getRegInfo();
const TargetRegisterInfo *tri = mf->getTarget().getRegisterInfo();
OwningPtr<PBQPRAProblem> p(new PBQPRAProblem());
PBQP::Graph &g = p->getGraph();
RegSet pregs;
// Collect the set of preg intervals, record that they're used in the MF.
for (unsigned Reg = 1, e = tri->getNumRegs(); Reg != e; ++Reg) {
if (mri->def_empty(Reg))
continue;
pregs.insert(Reg);
mri->setPhysRegUsed(Reg);
}
// Iterate over vregs.
for (RegSet::const_iterator vregItr = vregs.begin(), vregEnd = vregs.end();
vregItr != vregEnd; ++vregItr) {
unsigned vreg = *vregItr;
const TargetRegisterClass *trc = mri->getRegClass(vreg);
LiveInterval *vregLI = &LIS->getInterval(vreg);
// Record any overlaps with regmask operands.
BitVector regMaskOverlaps;
LIS->checkRegMaskInterference(*vregLI, regMaskOverlaps);
// Compute an initial allowed set for the current vreg.
typedef std::vector<unsigned> VRAllowed;
VRAllowed vrAllowed;
ArrayRef<uint16_t> rawOrder = trc->getRawAllocationOrder(*mf);
for (unsigned i = 0; i != rawOrder.size(); ++i) {
unsigned preg = rawOrder[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.
vrAllowed.push_back(preg);
}
// Construct the node.
PBQP::Graph::NodeItr node =
g.addNode(PBQP::Vector(vrAllowed.size() + 1, 0));
// Record the mapping and allowed set in the problem.
p->recordVReg(vreg, node, vrAllowed.begin(), vrAllowed.end());
PBQP::PBQPNum spillCost = (vregLI->weight != 0.0) ?
vregLI->weight : std::numeric_limits<PBQP::PBQPNum>::min();
addSpillCosts(g.getNodeCosts(node), spillCost);
}
for (RegSet::const_iterator vr1Itr = vregs.begin(), vrEnd = vregs.end();
vr1Itr != vrEnd; ++vr1Itr) {
unsigned vr1 = *vr1Itr;
const LiveInterval &l1 = lis->getInterval(vr1);
const PBQPRAProblem::AllowedSet &vr1Allowed = p->getAllowedSet(vr1);
for (RegSet::const_iterator vr2Itr = llvm::next(vr1Itr);
vr2Itr != vrEnd; ++vr2Itr) {
unsigned vr2 = *vr2Itr;
const LiveInterval &l2 = lis->getInterval(vr2);
const PBQPRAProblem::AllowedSet &vr2Allowed = p->getAllowedSet(vr2);
assert(!l2.empty() && "Empty interval in vreg set?");
if (l1.overlaps(l2)) {
PBQP::Graph::EdgeItr edge =
g.addEdge(p->getNodeForVReg(vr1), p->getNodeForVReg(vr2),
PBQP::Matrix(vr1Allowed.size()+1, vr2Allowed.size()+1, 0));
addInterferenceCosts(g.getEdgeCosts(edge), vr1Allowed, vr2Allowed, tri);
}
}
}
return p.take();
}
void PBQPBuilder::addSpillCosts(PBQP::Vector &costVec,
PBQP::PBQPNum spillCost) {
costVec[0] = spillCost;
}
void PBQPBuilder::addInterferenceCosts(
PBQP::Matrix &costMat,
const PBQPRAProblem::AllowedSet &vr1Allowed,
const PBQPRAProblem::AllowedSet &vr2Allowed,
const TargetRegisterInfo *tri) {
assert(costMat.getRows() == vr1Allowed.size() + 1 && "Matrix height mismatch.");
assert(costMat.getCols() == vr2Allowed.size() + 1 && "Matrix width mismatch.");
for (unsigned i = 0; i != vr1Allowed.size(); ++i) {
unsigned preg1 = vr1Allowed[i];
for (unsigned j = 0; j != vr2Allowed.size(); ++j) {
unsigned preg2 = vr2Allowed[j];
if (tri->regsOverlap(preg1, preg2)) {
costMat[i + 1][j + 1] = std::numeric_limits<PBQP::PBQPNum>::infinity();
}
}
}
}
PBQPRAProblem *PBQPBuilderWithCoalescing::build(MachineFunction *mf,
const LiveIntervals *lis,
const MachineBlockFrequencyInfo *mbfi,
const RegSet &vregs) {
OwningPtr<PBQPRAProblem> p(PBQPBuilder::build(mf, lis, mbfi, vregs));
PBQP::Graph &g = p->getGraph();
const TargetMachine &tm = mf->getTarget();
CoalescerPair cp(*tm.getRegisterInfo());
// Scan the machine function and add a coalescing cost whenever CoalescerPair
// gives the Ok.
for (MachineFunction::const_iterator mbbItr = mf->begin(),
mbbEnd = mf->end();
mbbItr != mbbEnd; ++mbbItr) {
const MachineBasicBlock *mbb = &*mbbItr;
for (MachineBasicBlock::const_iterator miItr = mbb->begin(),
miEnd = mbb->end();
miItr != miEnd; ++miItr) {
const MachineInstr *mi = &*miItr;
if (!cp.setRegisters(mi)) {
continue; // Not coalescable.
}
if (cp.getSrcReg() == cp.getDstReg()) {
continue; // Already coalesced.
}
unsigned dst = cp.getDstReg(),
src = cp.getSrcReg();
const float copyFactor = 0.5; // Cost of copy relative to load. Current
// value plucked randomly out of the air.
PBQP::PBQPNum cBenefit =
copyFactor * LiveIntervals::getSpillWeight(false, true,
mbfi->getBlockFreq(mbb));
if (cp.isPhys()) {
if (!mf->getRegInfo().isAllocatable(dst)) {
continue;
}
const PBQPRAProblem::AllowedSet &allowed = p->getAllowedSet(src);
unsigned pregOpt = 0;
while (pregOpt < allowed.size() && allowed[pregOpt] != dst) {
++pregOpt;
}
if (pregOpt < allowed.size()) {
++pregOpt; // +1 to account for spill option.
PBQP::Graph::NodeItr node = p->getNodeForVReg(src);
addPhysRegCoalesce(g.getNodeCosts(node), pregOpt, cBenefit);
}
} else {
const PBQPRAProblem::AllowedSet *allowed1 = &p->getAllowedSet(dst);
const PBQPRAProblem::AllowedSet *allowed2 = &p->getAllowedSet(src);
PBQP::Graph::NodeItr node1 = p->getNodeForVReg(dst);
PBQP::Graph::NodeItr node2 = p->getNodeForVReg(src);
PBQP::Graph::EdgeItr edge = g.findEdge(node1, node2);
if (edge == g.edgesEnd()) {
edge = g.addEdge(node1, node2, PBQP::Matrix(allowed1->size() + 1,
allowed2->size() + 1,
0));
} else {
if (g.getEdgeNode1(edge) == node2) {
std::swap(node1, node2);
std::swap(allowed1, allowed2);
}
}
addVirtRegCoalesce(g.getEdgeCosts(edge), *allowed1, *allowed2,
cBenefit);
}
}
}
return p.take();
}
void PBQPBuilderWithCoalescing::addPhysRegCoalesce(PBQP::Vector &costVec,
unsigned pregOption,
PBQP::PBQPNum benefit) {
costVec[pregOption] += -benefit;
}
void PBQPBuilderWithCoalescing::addVirtRegCoalesce(
PBQP::Matrix &costMat,
const PBQPRAProblem::AllowedSet &vr1Allowed,
const PBQPRAProblem::AllowedSet &vr2Allowed,
PBQP::PBQPNum benefit) {
assert(costMat.getRows() == vr1Allowed.size() + 1 && "Size mismatch.");
assert(costMat.getCols() == vr2Allowed.size() + 1 && "Size mismatch.");
for (unsigned i = 0; i != vr1Allowed.size(); ++i) {
unsigned preg1 = vr1Allowed[i];
for (unsigned j = 0; j != vr2Allowed.size(); ++j) {
unsigned preg2 = vr2Allowed[j];
if (preg1 == preg2) {
costMat[i + 1][j + 1] += -benefit;
}
}
}
}
void RegAllocPBQP::getAnalysisUsage(AnalysisUsage &au) const {
au.setPreservesCFG();
au.addRequired<AliasAnalysis>();
au.addPreserved<AliasAnalysis>();
au.addRequired<SlotIndexes>();
au.addPreserved<SlotIndexes>();
au.addRequired<LiveIntervals>();
au.addPreserved<LiveIntervals>();
//au.addRequiredID(SplitCriticalEdgesID);
if (customPassID)
au.addRequiredID(*customPassID);
au.addRequired<CalculateSpillWeights>();
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() {
// 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;
LiveInterval *li = &lis->getInterval(Reg);
// If this live interval is non-empty we will use pbqp to allocate it.
// Empty intervals we allocate in a simple post-processing stage in
// finalizeAlloc.
if (!li->empty()) {
vregsToAlloc.insert(li->reg);
} else {
emptyIntervalVRegs.insert(li->reg);
}
}
}
bool RegAllocPBQP::mapPBQPToRegAlloc(const PBQPRAProblem &problem,
const PBQP::Solution &solution) {
// Set to true if we have any spills
bool anotherRoundNeeded = false;
// Clear the existing allocation.
vrm->clearAllVirt();
const PBQP::Graph &g = problem.getGraph();
// Iterate over the nodes mapping the PBQP solution to a register
// assignment.
for (PBQP::Graph::ConstNodeItr node = g.nodesBegin(),
nodeEnd = g.nodesEnd();
node != nodeEnd; ++node) {
unsigned vreg = problem.getVRegForNode(node);
unsigned alloc = solution.getSelection(node);
if (problem.isPRegOption(vreg, alloc)) {
unsigned preg = problem.getPRegForOption(vreg, alloc);
DEBUG(dbgs() << "VREG " << PrintReg(vreg, tri) << " -> "
<< tri->getName(preg) << "\n");
assert(preg != 0 && "Invalid preg selected.");
vrm->assignVirt2Phys(vreg, preg);
} else if (problem.isSpillOption(vreg, alloc)) {
vregsToAlloc.erase(vreg);
SmallVector<LiveInterval*, 8> newSpills;
LiveRangeEdit LRE(&lis->getInterval(vreg), newSpills, *mf, *lis, vrm);
spiller->spill(LRE);
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 itr = LRE.begin(), end = LRE.end();
itr != end; ++itr) {
assert(!(*itr)->empty() && "Empty spill range.");
DEBUG(dbgs() << PrintReg((*itr)->reg, tri) << " ");
vregsToAlloc.insert((*itr)->reg);
}
DEBUG(dbgs() << ")\n");
// We need another round if spill intervals were added.
anotherRoundNeeded |= !LRE.empty();
} else {
llvm_unreachable("Unknown allocation option.");
}
}
return !anotherRoundNeeded;
}
void RegAllocPBQP::finalizeAlloc() const {
// First allocate registers for the empty intervals.
for (RegSet::const_iterator
itr = emptyIntervalVRegs.begin(), end = emptyIntervalVRegs.end();
itr != end; ++itr) {
LiveInterval *li = &lis->getInterval(*itr);
unsigned physReg = mri->getSimpleHint(li->reg);
if (physReg == 0) {
const TargetRegisterClass *liRC = mri->getRegClass(li->reg);
physReg = liRC->getRawAllocationOrder(*mf).front();
}
vrm->assignVirt2Phys(li->reg, physReg);
}
}
bool RegAllocPBQP::runOnMachineFunction(MachineFunction &MF) {
mf = &MF;
tm = &mf->getTarget();
tri = tm->getRegisterInfo();
tii = tm->getInstrInfo();
mri = &mf->getRegInfo();
lis = &getAnalysis<LiveIntervals>();
lss = &getAnalysis<LiveStacks>();
mbfi = &getAnalysis<MachineBlockFrequencyInfo>();
vrm = &getAnalysis<VirtRegMap>();
spiller.reset(createInlineSpiller(*this, MF, *vrm));
mri->freezeReservedRegs(MF);
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();
#ifndef NDEBUG
const Function* func = mf->getFunction();
std::string fqn =
func->getParent()->getModuleIdentifier() + "." +
func->getName().str();
#endif
// If there are non-empty intervals allocate them using pbqp.
if (!vregsToAlloc.empty()) {
bool pbqpAllocComplete = false;
unsigned round = 0;
while (!pbqpAllocComplete) {
DEBUG(dbgs() << " PBQP Regalloc round " << round << ":\n");
OwningPtr<PBQPRAProblem> problem(
builder->build(mf, lis, mbfi, vregsToAlloc));
#ifndef NDEBUG
if (pbqpDumpGraphs) {
std::ostringstream rs;
rs << round;
std::string graphFileName(fqn + "." + rs.str() + ".pbqpgraph");
std::string tmp;
raw_fd_ostream os(graphFileName.c_str(), tmp);
DEBUG(dbgs() << "Dumping graph for round " << round << " to \""
<< graphFileName << "\"\n");
problem->getGraph().dump(os);
}
#endif
PBQP::Solution solution =
PBQP::HeuristicSolver<PBQP::Heuristics::Briggs>::solve(
problem->getGraph());
pbqpAllocComplete = mapPBQPToRegAlloc(*problem, solution);
++round;
}
}
// Finalise allocation, allocate empty ranges.
finalizeAlloc();
vregsToAlloc.clear();
emptyIntervalVRegs.clear();
DEBUG(dbgs() << "Post alloc VirtRegMap:\n" << *vrm << "\n");
return true;
}
FunctionPass* llvm::createPBQPRegisterAllocator(
OwningPtr<PBQPBuilder> &builder,
char *customPassID) {
return new RegAllocPBQP(builder, customPassID);
}
FunctionPass* llvm::createDefaultPBQPRegisterAllocator() {
OwningPtr<PBQPBuilder> Builder;
if (pbqpCoalescing)
Builder.reset(new PBQPBuilderWithCoalescing());
else
Builder.reset(new PBQPBuilder());
return createPBQPRegisterAllocator(Builder);
}
#undef DEBUG_TYPE