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

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//===------ 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 "PBQP/HeuristicSolver.h"
#include "PBQP/SimpleGraph.h"
#include "PBQP/Heuristics/Briggs.h"
#include "VirtRegMap.h"
#include "VirtRegRewriter.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/LiveStackAnalysis.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/RegAllocRegistry.h"
#include "llvm/CodeGen/RegisterCoalescer.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 <map>
#include <memory>
#include <set>
#include <vector>
using namespace llvm;
static RegisterRegAlloc
registerPBQPRepAlloc("pbqp", "PBQP register allocator.",
llvm::createPBQPRegisterAllocator);
namespace {
///
/// PBQP based allocators solve the register allocation problem by mapping
/// register allocation problems to Partitioned Boolean Quadratic
/// Programming problems.
class VISIBILITY_HIDDEN PBQPRegAlloc : public MachineFunctionPass {
public:
static char ID;
/// Construct a PBQP register allocator.
PBQPRegAlloc() : MachineFunctionPass((intptr_t)&ID) {}
/// Return the pass name.
virtual const char* getPassName() const throw() {
return "PBQP Register Allocator";
}
/// PBQP analysis usage.
virtual void getAnalysisUsage(AnalysisUsage &au) const {
au.addRequired<LiveIntervals>();
//au.addRequiredID(SplitCriticalEdgesID);
au.addRequired<LiveStacks>();
au.addPreserved<LiveStacks>();
au.addRequired<MachineLoopInfo>();
au.addPreserved<MachineLoopInfo>();
au.addRequired<VirtRegMap>();
MachineFunctionPass::getAnalysisUsage(au);
}
/// 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::set<unsigned> RegSet;
typedef std::pair<unsigned, unsigned> RegPair;
typedef std::map<RegPair, PBQP::PBQPNum> CoalesceMap;
typedef std::set<LiveInterval*> LiveIntervalSet;
MachineFunction *mf;
const TargetMachine *tm;
const TargetRegisterInfo *tri;
const TargetInstrInfo *tii;
const MachineLoopInfo *loopInfo;
MachineRegisterInfo *mri;
LiveIntervals *lis;
LiveStacks *lss;
VirtRegMap *vrm;
LI2NodeMap li2Node;
Node2LIMap node2LI;
AllowedSetMap allowedSets;
LiveIntervalSet vregIntervalsToAlloc,
emptyVRegIntervals;
/// Builds a PBQP cost vector.
template <typename RegContainer>
PBQP::Vector buildCostVector(unsigned vReg,
const RegContainer &allowed,
const CoalesceMap &cealesces,
PBQP::PBQPNum spillCost) const;
/// \brief Builds a PBQP interference matrix.
///
/// @return Either a pointer to a non-zero PBQP matrix representing the
/// allocation option costs, or a null pointer for a zero matrix.
///
/// Expects allowed sets for two interfering LiveIntervals. These allowed
/// sets should contain only allocable registers from the LiveInterval's
/// register class, with any interfering pre-colored registers removed.
template <typename RegContainer>
PBQP::Matrix* buildInterferenceMatrix(const RegContainer &allowed1,
const RegContainer &allowed2) const;
///
/// Expects allowed sets for two potentially coalescable LiveIntervals,
/// and an estimated benefit due to coalescing. The allowed sets should
/// contain only allocable registers from the LiveInterval's register
/// classes, with any interfering pre-colored registers removed.
template <typename RegContainer>
PBQP::Matrix* buildCoalescingMatrix(const RegContainer &allowed1,
const RegContainer &allowed2,
PBQP::PBQPNum cBenefit) const;
/// \brief Finds coalescing opportunities and returns them as a map.
///
/// Any entries in the map are guaranteed coalescable, even if their
/// corresponding live intervals overlap.
CoalesceMap findCoalesces();
/// \brief Finds the initial set of vreg intervals to allocate.
void findVRegIntervalsToAlloc();
/// \brief Constructs a PBQP problem representation of the register
/// allocation problem for this function.
///
/// @return a PBQP solver object for the register allocation problem.
PBQP::SimpleGraph constructPBQPProblem();
/// \brief Adds a stack interval if the given live interval has been
/// spilled. Used to support stack slot coloring.
void addStackInterval(const LiveInterval *spilled,MachineRegisterInfo* mri);
/// \brief Given a solved PBQP problem maps this solution back to a register
/// assignment.
bool mapPBQPToRegAlloc(const PBQP::Solution &solution);
/// \brief Postprocessing before final spilling. Sets basic block "live in"
/// variables.
void finalizeAlloc() const;
};
char PBQPRegAlloc::ID = 0;
}
template <typename RegContainer>
PBQP::Vector PBQPRegAlloc::buildCostVector(unsigned vReg,
const RegContainer &allowed,
const CoalesceMap &coalesces,
PBQP::PBQPNum spillCost) const {
typedef typename RegContainer::const_iterator AllowedItr;
// Allocate vector. Additional element (0th) used for spill option
PBQP::Vector v(allowed.size() + 1, 0);
v[0] = spillCost;
// Iterate over the allowed registers inserting coalesce benefits if there
// are any.
unsigned ai = 0;
for (AllowedItr itr = allowed.begin(), end = allowed.end();
itr != end; ++itr, ++ai) {
unsigned pReg = *itr;
CoalesceMap::const_iterator cmItr =
coalesces.find(RegPair(vReg, pReg));
// No coalesce - on to the next preg.
if (cmItr == coalesces.end())
continue;
// We have a coalesce - insert the benefit.
v[ai + 1] = -cmItr->second;
}
return v;
}
template <typename RegContainer>
PBQP::Matrix* PBQPRegAlloc::buildInterferenceMatrix(
const RegContainer &allowed1, const RegContainer &allowed2) const {
typedef typename RegContainer::const_iterator RegContainerIterator;
// Construct a PBQP matrix representing the cost of allocation options. The
// rows and columns correspond to the allocation options for the two live
// intervals. Elements will be infinite where corresponding registers alias,
// since we cannot allocate aliasing registers to interfering live intervals.
// All other elements (non-aliasing combinations) will have zero cost. Note
// that the spill option (element 0,0) has zero cost, since we can allocate
// both intervals to memory safely (the cost for each individual allocation
// to memory is accounted for by the cost vectors for each live interval).
PBQP::Matrix *m =
new PBQP::Matrix(allowed1.size() + 1, allowed2.size() + 1, 0);
// Assume this is a zero matrix until proven otherwise. Zero matrices occur
// between interfering live ranges with non-overlapping register sets (e.g.
// non-overlapping reg classes, or disjoint sets of allowed regs within the
// same class). The term "overlapping" is used advisedly: sets which do not
// intersect, but contain registers which alias, will have non-zero matrices.
// We optimize zero matrices away to improve solver speed.
bool isZeroMatrix = true;
// Row index. Starts at 1, since the 0th row is for the spill option, which
// is always zero.
unsigned ri = 1;
// Iterate over allowed sets, insert infinities where required.
for (RegContainerIterator a1Itr = allowed1.begin(), a1End = allowed1.end();
a1Itr != a1End; ++a1Itr) {
// Column index, starts at 1 as for row index.
unsigned ci = 1;
unsigned reg1 = *a1Itr;
for (RegContainerIterator a2Itr = allowed2.begin(), a2End = allowed2.end();
a2Itr != a2End; ++a2Itr) {
unsigned reg2 = *a2Itr;
// If the row/column regs are identical or alias insert an infinity.
if ((reg1 == reg2) || tri->areAliases(reg1, reg2)) {
(*m)[ri][ci] = std::numeric_limits<PBQP::PBQPNum>::infinity();
isZeroMatrix = false;
}
++ci;
}
++ri;
}
// If this turns out to be a zero matrix...
if (isZeroMatrix) {
// free it and return null.
delete m;
return 0;
}
// ...otherwise return the cost matrix.
return m;
}
template <typename RegContainer>
PBQP::Matrix* PBQPRegAlloc::buildCoalescingMatrix(
const RegContainer &allowed1, const RegContainer &allowed2,
PBQP::PBQPNum cBenefit) const {
typedef typename RegContainer::const_iterator RegContainerIterator;
// Construct a PBQP Matrix representing the benefits of coalescing. As with
// interference matrices the rows and columns represent allowed registers
// for the LiveIntervals which are (potentially) to be coalesced. The amount
// -cBenefit will be placed in any element representing the same register
// for both intervals.
PBQP::Matrix *m =
new PBQP::Matrix(allowed1.size() + 1, allowed2.size() + 1, 0);
// Reset costs to zero.
m->reset(0);
// Assume the matrix is zero till proven otherwise. Zero matrices will be
// optimized away as in the interference case.
bool isZeroMatrix = true;
// Row index. Starts at 1, since the 0th row is for the spill option, which
// is always zero.
unsigned ri = 1;
// Iterate over the allowed sets, insert coalescing benefits where
// appropriate.
for (RegContainerIterator a1Itr = allowed1.begin(), a1End = allowed1.end();
a1Itr != a1End; ++a1Itr) {
// Column index, starts at 1 as for row index.
unsigned ci = 1;
unsigned reg1 = *a1Itr;
for (RegContainerIterator a2Itr = allowed2.begin(), a2End = allowed2.end();
a2Itr != a2End; ++a2Itr) {
// If the row and column represent the same register insert a beneficial
// cost to preference this allocation - it would allow us to eliminate a
// move instruction.
if (reg1 == *a2Itr) {
(*m)[ri][ci] = -cBenefit;
isZeroMatrix = false;
}
++ci;
}
++ri;
}
// If this turns out to be a zero matrix...
if (isZeroMatrix) {
// ...free it and return null.
delete m;
return 0;
}
return m;
}
PBQPRegAlloc::CoalesceMap PBQPRegAlloc::findCoalesces() {
typedef MachineFunction::const_iterator MFIterator;
typedef MachineBasicBlock::const_iterator MBBIterator;
typedef LiveInterval::const_vni_iterator VNIIterator;
CoalesceMap coalescesFound;
// To find coalesces we need to iterate over the function looking for
// copy instructions.
for (MFIterator bbItr = mf->begin(), bbEnd = mf->end();
bbItr != bbEnd; ++bbItr) {
const MachineBasicBlock *mbb = &*bbItr;
for (MBBIterator iItr = mbb->begin(), iEnd = mbb->end();
iItr != iEnd; ++iItr) {
const MachineInstr *instr = &*iItr;
unsigned srcReg, dstReg, srcSubReg, dstSubReg;
// If this isn't a copy then continue to the next instruction.
if (!tii->isMoveInstr(*instr, srcReg, dstReg, srcSubReg, dstSubReg))
continue;
// If the registers are already the same our job is nice and easy.
if (dstReg == srcReg)
continue;
bool srcRegIsPhysical = TargetRegisterInfo::isPhysicalRegister(srcReg),
dstRegIsPhysical = TargetRegisterInfo::isPhysicalRegister(dstReg);
// If both registers are physical then we can't coalesce.
if (srcRegIsPhysical && dstRegIsPhysical)
continue;
// If it's a copy that includes a virtual register but the source and
// destination classes differ then we can't coalesce, so continue with
// the next instruction.
const TargetRegisterClass *srcRegClass = srcRegIsPhysical ?
tri->getPhysicalRegisterRegClass(srcReg) : mri->getRegClass(srcReg);
const TargetRegisterClass *dstRegClass = dstRegIsPhysical ?
tri->getPhysicalRegisterRegClass(dstReg) : mri->getRegClass(dstReg);
if (srcRegClass != dstRegClass)
continue;
// We also need any physical regs to be allocable, coalescing with
// a non-allocable register is invalid.
if (srcRegIsPhysical) {
if (std::find(srcRegClass->allocation_order_begin(*mf),
srcRegClass->allocation_order_end(*mf), srcReg) ==
srcRegClass->allocation_order_end(*mf))
continue;
}
if (dstRegIsPhysical) {
if (std::find(dstRegClass->allocation_order_begin(*mf),
dstRegClass->allocation_order_end(*mf), dstReg) ==
dstRegClass->allocation_order_end(*mf))
continue;
}
// If we've made it here we have a copy with compatible register classes.
// We can probably coalesce, but we need to consider overlap.
const LiveInterval *srcLI = &lis->getInterval(srcReg),
*dstLI = &lis->getInterval(dstReg);
if (srcLI->overlaps(*dstLI)) {
// Even in the case of an overlap we might still be able to coalesce,
// but we need to make sure that no definition of either range occurs
// while the other range is live.
// Otherwise start by assuming we're ok.
bool badDef = false;
// Test all defs of the source range.
for (VNIIterator
vniItr = srcLI->vni_begin(), vniEnd = srcLI->vni_end();
vniItr != vniEnd; ++vniItr) {
// If we find a def that kills the coalescing opportunity then
// record it and break from the loop.
if (dstLI->liveAt((*vniItr)->def)) {
badDef = true;
break;
}
}
// If we have a bad def give up, continue to the next instruction.
if (badDef)
continue;
// Otherwise test definitions of the destination range.
for (VNIIterator
vniItr = dstLI->vni_begin(), vniEnd = dstLI->vni_end();
vniItr != vniEnd; ++vniItr) {
// We want to make sure we skip the copy instruction itself.
if ((*vniItr)->copy == instr)
continue;
if (srcLI->liveAt((*vniItr)->def)) {
badDef = true;
break;
}
}
// As before a bad def we give up and continue to the next instr.
if (badDef)
continue;
}
// If we make it to here then either the ranges didn't overlap, or they
// did, but none of their definitions would prevent us from coalescing.
// We're good to go with the coalesce.
float cBenefit = powf(10.0f, loopInfo->getLoopDepth(mbb)) / 5.0;
coalescesFound[RegPair(srcReg, dstReg)] = cBenefit;
coalescesFound[RegPair(dstReg, srcReg)] = cBenefit;
}
}
return coalescesFound;
}
void PBQPRegAlloc::findVRegIntervalsToAlloc() {
// Iterate over all live ranges.
for (LiveIntervals::iterator itr = lis->begin(), end = lis->end();
itr != end; ++itr) {
// Ignore physical ones.
if (TargetRegisterInfo::isPhysicalRegister(itr->first))
continue;
LiveInterval *li = itr->second;
// 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()) {
vregIntervalsToAlloc.insert(li);
}
else {
emptyVRegIntervals.insert(li);
}
}
}
PBQP::SimpleGraph PBQPRegAlloc::constructPBQPProblem() {
typedef std::vector<const LiveInterval*> LIVector;
typedef std::vector<unsigned> RegVector;
typedef std::vector<PBQP::SimpleGraph::NodeIterator> NodeVector;
// This will store the physical intervals for easy reference.
LIVector physIntervals;
// Start by clearing the old node <-> live interval mappings & allowed sets
li2Node.clear();
node2LI.clear();
allowedSets.clear();
// Populate physIntervals, update preg use:
for (LiveIntervals::iterator itr = lis->begin(), end = lis->end();
itr != end; ++itr) {
if (TargetRegisterInfo::isPhysicalRegister(itr->first)) {
physIntervals.push_back(itr->second);
mri->setPhysRegUsed(itr->second->reg);
}
}
// Iterate over vreg intervals, construct live interval <-> node number
// mappings.
for (LiveIntervalSet::const_iterator
itr = vregIntervalsToAlloc.begin(), end = vregIntervalsToAlloc.end();
itr != end; ++itr) {
const LiveInterval *li = *itr;
li2Node[li] = node2LI.size();
node2LI.push_back(li);
}
// Get the set of potential coalesces.
CoalesceMap coalesces;//(findCoalesces());
// Construct a PBQP solver for this problem
PBQP::SimpleGraph problem;
NodeVector problemNodes(vregIntervalsToAlloc.size());
// Resize allowedSets container appropriately.
allowedSets.resize(vregIntervalsToAlloc.size());
// Iterate over virtual register intervals to compute allowed sets...
for (unsigned node = 0; node < node2LI.size(); ++node) {
// Grab pointers to the interval and its register class.
const LiveInterval *li = node2LI[node];
const TargetRegisterClass *liRC = mri->getRegClass(li->reg);
// Start by assuming all allocable registers in the class are allowed...
RegVector liAllowed(liRC->allocation_order_begin(*mf),
liRC->allocation_order_end(*mf));
// Eliminate the physical registers which overlap with this range, along
// with all their aliases.
for (LIVector::iterator pItr = physIntervals.begin(),
pEnd = physIntervals.end(); pItr != pEnd; ++pItr) {
if (!li->overlaps(**pItr))
continue;
unsigned pReg = (*pItr)->reg;
// If we get here then the live intervals overlap, but we're still ok
// if they're coalescable.
if (coalesces.find(RegPair(li->reg, pReg)) != coalesces.end())
continue;
// If we get here then we have a genuine exclusion.
// Remove the overlapping reg...
RegVector::iterator eraseItr =
std::find(liAllowed.begin(), liAllowed.end(), pReg);
if (eraseItr != liAllowed.end())
liAllowed.erase(eraseItr);
const unsigned *aliasItr = tri->getAliasSet(pReg);
if (aliasItr != 0) {
// ...and its aliases.
for (; *aliasItr != 0; ++aliasItr) {
RegVector::iterator eraseItr =
std::find(liAllowed.begin(), liAllowed.end(), *aliasItr);
if (eraseItr != liAllowed.end()) {
liAllowed.erase(eraseItr);
}
}
}
}
// Copy the allowed set into a member vector for use when constructing cost
// vectors & matrices, and mapping PBQP solutions back to assignments.
allowedSets[node] = AllowedSet(liAllowed.begin(), liAllowed.end());
// Set the spill cost to the interval weight, or epsilon if the
// interval weight is zero
PBQP::PBQPNum spillCost = (li->weight != 0.0) ?
li->weight : std::numeric_limits<PBQP::PBQPNum>::min();
// Build a cost vector for this interval.
problemNodes[node] =
problem.addNode(
buildCostVector(li->reg, allowedSets[node], coalesces, spillCost));
}
// Now add the cost matrices...
for (unsigned node1 = 0; node1 < node2LI.size(); ++node1) {
const LiveInterval *li = node2LI[node1];
// Test for live range overlaps and insert interference matrices.
for (unsigned node2 = node1 + 1; node2 < node2LI.size(); ++node2) {
const LiveInterval *li2 = node2LI[node2];
CoalesceMap::const_iterator cmItr =
coalesces.find(RegPair(li->reg, li2->reg));
PBQP::Matrix *m = 0;
if (cmItr != coalesces.end()) {
m = buildCoalescingMatrix(allowedSets[node1], allowedSets[node2],
cmItr->second);
}
else if (li->overlaps(*li2)) {
m = buildInterferenceMatrix(allowedSets[node1], allowedSets[node2]);
}
if (m != 0) {
problem.addEdge(problemNodes[node1],
problemNodes[node2],
*m);
delete m;
}
}
}
problem.assignNodeIDs();
assert(problem.getNumNodes() == allowedSets.size());
for (unsigned i = 0; i < allowedSets.size(); ++i) {
assert(problem.getNodeItr(i) == problemNodes[i]);
}
/*
std::cerr << "Allocating for " << problem.getNumNodes() << " nodes, "
<< problem.getNumEdges() << " edges.\n";
problem.printDot(std::cerr);
*/
// We're done, PBQP problem constructed - return it.
return problem;
}
void PBQPRegAlloc::addStackInterval(const LiveInterval *spilled,
MachineRegisterInfo* mri) {
int stackSlot = vrm->getStackSlot(spilled->reg);
if (stackSlot == VirtRegMap::NO_STACK_SLOT)
return;
const TargetRegisterClass *RC = mri->getRegClass(spilled->reg);
LiveInterval &stackInterval = lss->getOrCreateInterval(stackSlot, RC);
VNInfo *vni;
if (stackInterval.getNumValNums() != 0)
vni = stackInterval.getValNumInfo(0);
else
vni = stackInterval.getNextValue(0, 0, false, lss->getVNInfoAllocator());
LiveInterval &rhsInterval = lis->getInterval(spilled->reg);
stackInterval.MergeRangesInAsValue(rhsInterval, vni);
}
bool PBQPRegAlloc::mapPBQPToRegAlloc(const PBQP::Solution &solution) {
static unsigned round = 0;
(void) round;
// Set to true if we have any spills
bool anotherRoundNeeded = false;
// Clear the existing allocation.
vrm->clearAllVirt();
CoalesceMap coalesces;//(findCoalesces());
for (unsigned i = 0; i < node2LI.size(); ++i) {
if (solution.getSelection(i) == 0) {
continue;
}
unsigned iSel = solution.getSelection(i);
unsigned iAlloc = allowedSets[i][iSel - 1];
for (unsigned j = i + 1; j < node2LI.size(); ++j) {
if (solution.getSelection(j) == 0) {
continue;
}
unsigned jSel = solution.getSelection(j);
unsigned jAlloc = allowedSets[j][jSel - 1];
if ((iAlloc != jAlloc) && !tri->areAliases(iAlloc, jAlloc)) {
continue;
}
if (node2LI[i]->overlaps(*node2LI[j])) {
if (coalesces.find(RegPair(node2LI[i]->reg, node2LI[j]->reg)) == coalesces.end()) {
DEBUG(errs() << "In round " << ++round << ":\n"
<< "Bogusness in " << mf->getFunction()->getName() << "!\n"
<< "Live interval " << i << " (reg" << node2LI[i]->reg << ") and\n"
<< "Live interval " << j << " (reg" << node2LI[j]->reg << ")\n"
<< " were allocated registers " << iAlloc << " (index " << iSel << ") and "
<< jAlloc << "(index " << jSel
<< ") respectively in a graph of " << solution.numNodes() << " nodes.\n"
<< "li[i]->empty() = " << node2LI[i]->empty() << "\n"
<< "li[j]->empty() = " << node2LI[j]->empty() << "\n"
<< "li[i]->overlaps(li[j]) = " << node2LI[i]->overlaps(*node2LI[j]) << "\n"
<< "coalesce = " << (coalesces.find(RegPair(node2LI[i]->reg, node2LI[j]->reg)) != coalesces.end()) << "\n");
DEBUG(errs() << "solution.getCost() = " << solution.getCost() << "\n");
exit(1);
}
}
}
}
// Iterate over the nodes mapping the PBQP solution to a register assignment.
for (unsigned node = 0; node < node2LI.size(); ++node) {
unsigned virtReg = node2LI[node]->reg,
allocSelection = solution.getSelection(node);
// If the PBQP solution is non-zero it's a physical register...
if (allocSelection != 0) {
// Get the physical reg, subtracting 1 to account for the spill option.
unsigned physReg = allowedSets[node][allocSelection - 1];
DOUT << "VREG " << virtReg << " -> " << tri->getName(physReg) << "\n";
assert(physReg != 0);
// Add to the virt reg map and update the used phys regs.
vrm->assignVirt2Phys(virtReg, physReg);
}
// ...Otherwise it's a spill.
else {
// Make sure we ignore this virtual reg on the next round
// of allocation
vregIntervalsToAlloc.erase(&lis->getInterval(virtReg));
// Insert spill ranges for this live range
const LiveInterval *spillInterval = node2LI[node];
double oldSpillWeight = spillInterval->weight;
SmallVector<LiveInterval*, 8> spillIs;
std::vector<LiveInterval*> newSpills =
lis->addIntervalsForSpills(*spillInterval, spillIs, loopInfo, *vrm);
addStackInterval(spillInterval, mri);
DOUT << "VREG " << virtReg << " -> SPILLED (Cost: "
<< oldSpillWeight << ", New vregs: ";
// Copy any newly inserted live intervals into the list of regs to
// allocate.
for (std::vector<LiveInterval*>::const_iterator
itr = newSpills.begin(), end = newSpills.end();
itr != end; ++itr) {
assert(!(*itr)->empty() && "Empty spill range.");
DOUT << (*itr)->reg << " ";
vregIntervalsToAlloc.insert(*itr);
}
DOUT << ")\n";
// We need another round if spill intervals were added.
anotherRoundNeeded |= !newSpills.empty();
}
}
return !anotherRoundNeeded;
}
void PBQPRegAlloc::finalizeAlloc() const {
typedef LiveIntervals::iterator LIIterator;
typedef LiveInterval::Ranges::const_iterator LRIterator;
// First allocate registers for the empty intervals.
for (LiveIntervalSet::const_iterator
itr = emptyVRegIntervals.begin(), end = emptyVRegIntervals.end();
itr != end; ++itr) {
LiveInterval *li = *itr;
unsigned physReg = vrm->getRegAllocPref(li->reg);
if (physReg == 0) {
const TargetRegisterClass *liRC = mri->getRegClass(li->reg);
physReg = *liRC->allocation_order_begin(*mf);
}
vrm->assignVirt2Phys(li->reg, physReg);
}
// Finally iterate over the basic blocks to compute and set the live-in sets.
SmallVector<MachineBasicBlock*, 8> liveInMBBs;
MachineBasicBlock *entryMBB = &*mf->begin();
for (LIIterator liItr = lis->begin(), liEnd = lis->end();
liItr != liEnd; ++liItr) {
const LiveInterval *li = liItr->second;
unsigned reg = 0;
// Get the physical register for this interval
if (TargetRegisterInfo::isPhysicalRegister(li->reg)) {
reg = li->reg;
}
else if (vrm->isAssignedReg(li->reg)) {
reg = vrm->getPhys(li->reg);
}
else {
// Ranges which are assigned a stack slot only are ignored.
continue;
}
if (reg == 0) {
// Filter out zero regs - they're for intervals that were spilled.
continue;
}
// Iterate over the ranges of the current interval...
for (LRIterator lrItr = li->begin(), lrEnd = li->end();
lrItr != lrEnd; ++lrItr) {
// Find the set of basic blocks which this range is live into...
if (lis->findLiveInMBBs(lrItr->start, lrItr->end, liveInMBBs)) {
// And add the physreg for this interval to their live-in sets.
for (unsigned i = 0; i < liveInMBBs.size(); ++i) {
if (liveInMBBs[i] != entryMBB) {
if (!liveInMBBs[i]->isLiveIn(reg)) {
liveInMBBs[i]->addLiveIn(reg);
}
}
}
liveInMBBs.clear();
}
}
}
}
bool PBQPRegAlloc::runOnMachineFunction(MachineFunction &MF) {
mf = &MF;
tm = &mf->getTarget();
tri = tm->getRegisterInfo();
tii = tm->getInstrInfo();
mri = &mf->getRegInfo();
lis = &getAnalysis<LiveIntervals>();
lss = &getAnalysis<LiveStacks>();
loopInfo = &getAnalysis<MachineLoopInfo>();
vrm = &getAnalysis<VirtRegMap>();
DEBUG(errs() << "PBQP2 Register Allocating for " << mf->getFunction()->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();
// If there aren't any then we're done here.
if (vregIntervalsToAlloc.empty() && emptyVRegIntervals.empty())
return true;
// If there are non-empty intervals allocate them using pbqp.
if (!vregIntervalsToAlloc.empty()) {
bool pbqpAllocComplete = false;
unsigned round = 0;
while (!pbqpAllocComplete) {
DEBUG(errs() << " PBQP Regalloc round " << round << ":\n");
PBQP::SimpleGraph problem = constructPBQPProblem();
PBQP::HeuristicSolver<PBQP::Heuristics::Briggs> solver;
problem.assignNodeIDs();
PBQP::Solution solution = solver.solve(problem);
/*
std::cerr << "Solution:\n";
for (unsigned i = 0; i < solution.numNodes(); ++i) {
std::cerr << " " << i << " -> " << solution.getSelection(i) << "\n";
}
*/
pbqpAllocComplete = mapPBQPToRegAlloc(solution);
++round;
}
}
// Finalise allocation, allocate empty ranges.
finalizeAlloc();
vregIntervalsToAlloc.clear();
emptyVRegIntervals.clear();
li2Node.clear();
node2LI.clear();
allowedSets.clear();
DEBUG(errs() << "Post alloc VirtRegMap:\n" << *vrm << "\n");
// Run rewriter
std::auto_ptr<VirtRegRewriter> rewriter(createVirtRegRewriter());
rewriter->runOnMachineFunction(*mf, *vrm, lis);
return true;
}
FunctionPass* llvm::createPBQPRegisterAllocator() {
return new PBQPRegAlloc();
}
#undef DEBUG_TYPE
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