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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 "RenderMachineFunction.h"
#include "Splitter.h"
#include "VirtRegMap.h"
#include "VirtRegRewriter.h"
#include "llvm/CodeGen/CalcSpillWeights.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/LiveStackAnalysis.h"
#include "llvm/CodeGen/RegAllocPBQP.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/PBQP/HeuristicSolver.h"
#include "llvm/CodeGen/PBQP/Graph.h"
#include "llvm/CodeGen/PBQP/Heuristics/Briggs.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 <memory>
#include <set>
#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);
static cl::opt<bool>
pbqpBuilder("pbqp-builder",
cl::desc("Use new builder system."),
cl::init(true), cl::Hidden);
static cl::opt<bool>
pbqpPreSplitting("pbqp-pre-splitting",
cl::desc("Pre-split before PBQP register allocation."),
cl::init(false), cl::Hidden);
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(std::auto_ptr<PBQPBuilder> b) : MachineFunctionPass(ID), builder(b) {}
/// 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::vector<PBQP::Graph::NodeItr> NodeVector;
typedef std::set<unsigned> RegSet;
std::auto_ptr<PBQPBuilder> builder;
MachineFunction *mf;
const TargetMachine *tm;
const TargetRegisterInfo *tri;
const TargetInstrInfo *tii;
const MachineLoopInfo *loopInfo;
MachineRegisterInfo *mri;
RenderMachineFunction *rmf;
LiveIntervals *lis;
LiveStacks *lss;
VirtRegMap *vrm;
LI2NodeMap li2Node;
Node2LIMap node2LI;
AllowedSetMap allowedSets;
RegSet vregsToAlloc, emptyIntervalVRegs;
NodeVector problemNodes;
/// 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.
///
/// Old Construction Process - this functionality has been subsumed
/// by PBQPBuilder. This function will only be hanging around for a little
/// while until the new system has been fully tested.
///
/// @return a PBQP solver object for the register allocation problem.
PBQP::Graph constructPBQPProblemOld();
/// \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.
///
/// Old Construction Process - this functionality has been subsumed
/// by PBQPBuilder. This function will only be hanging around for a little
/// while until the new system has been fully tested.
///
bool mapPBQPToRegAllocOld(const PBQP::Solution &solution);
/// \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];
}
std::auto_ptr<PBQPRAProblem> PBQPBuilder::build(MachineFunction *mf,
const LiveIntervals *lis,
const MachineLoopInfo *loopInfo,
const RegSet &vregs) {
typedef std::vector<const LiveInterval*> LIVector;
MachineRegisterInfo *mri = &mf->getRegInfo();
const TargetRegisterInfo *tri = mf->getTarget().getRegisterInfo();
std::auto_ptr<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 (LiveIntervals::const_iterator itr = lis->begin(), end = lis->end();
itr != end; ++itr) {
if (TargetRegisterInfo::isPhysicalRegister(itr->first)) {
pregs.insert(itr->first);
mri->setPhysRegUsed(itr->first);
}
}
BitVector reservedRegs = tri->getReservedRegs(*mf);
// 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);
const LiveInterval *vregLI = &lis->getInterval(vreg);
// Compute an initial allowed set for the current vreg.
typedef std::vector<unsigned> VRAllowed;
VRAllowed vrAllowed;
for (TargetRegisterClass::iterator aoItr = trc->allocation_order_begin(*mf),
aoEnd = trc->allocation_order_end(*mf);
aoItr != aoEnd; ++aoItr) {
unsigned preg = *aoItr;
if (!reservedRegs.test(preg)) {
vrAllowed.push_back(preg);
}
}
// Remove any physical registers which overlap.
for (RegSet::const_iterator pregItr = pregs.begin(),
pregEnd = pregs.end();
pregItr != pregEnd; ++pregItr) {
unsigned preg = *pregItr;
const LiveInterval *pregLI = &lis->getInterval(preg);
if (pregLI->empty())
continue;
if (!vregLI->overlaps(*pregLI))
continue;
// Remove the register from the allowed set.
VRAllowed::iterator eraseItr =
std::find(vrAllowed.begin(), vrAllowed.end(), preg);
if (eraseItr != vrAllowed.end()) {
vrAllowed.erase(eraseItr);
}
// Also remove any aliases.
const unsigned *aliasItr = tri->getAliasSet(preg);
if (aliasItr != 0) {
for (; *aliasItr != 0; ++aliasItr) {
VRAllowed::iterator eraseItr =
std::find(vrAllowed.begin(), vrAllowed.end(), *aliasItr);
if (eraseItr != vrAllowed.end()) {
vrAllowed.erase(eraseItr);
}
}
}
}
// 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;
}
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();
}
}
}
}
std::auto_ptr<PBQPRAProblem> PBQPBuilderWithCoalescing::build(
MachineFunction *mf,
const LiveIntervals *lis,
const MachineLoopInfo *loopInfo,
const RegSet &vregs) {
std::auto_ptr<PBQPRAProblem> p = PBQPBuilder::build(mf, lis, loopInfo, vregs);
PBQP::Graph &g = p->getGraph();
const TargetMachine &tm = mf->getTarget();
CoalescerPair cp(*tm.getInstrInfo(), *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,
loopInfo->getLoopDepth(mbb));
if (cp.isPhys()) {
if (!lis->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;
}
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.addRequired<SlotIndexes>();
au.addPreserved<SlotIndexes>();
au.addRequired<LiveIntervals>();
//au.addRequiredID(SplitCriticalEdgesID);
au.addRequired<RegisterCoalescer>();
au.addRequired<CalculateSpillWeights>();
au.addRequired<LiveStacks>();
au.addPreserved<LiveStacks>();
au.addRequired<MachineLoopInfo>();
au.addPreserved<MachineLoopInfo>();
if (pbqpPreSplitting)
au.addRequired<LoopSplitter>();
au.addRequired<VirtRegMap>();
au.addRequired<RenderMachineFunction>();
MachineFunctionPass::getAnalysisUsage(au);
}
template <typename RegContainer>
PBQP::Vector RegAllocPBQP::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* RegAllocPBQP::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 (tri->regsOverlap(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* RegAllocPBQP::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;
}
RegAllocPBQP::CoalesceMap RegAllocPBQP::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;
// If this isn't a copy then continue to the next instruction.
if (!instr->isCopy())
continue;
unsigned srcReg = instr->getOperand(1).getReg();
unsigned dstReg = instr->getOperand(0).getReg();
// 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 two virtual register but the source and
// destination classes differ then we can't coalesce.
if (!srcRegIsPhysical && !dstRegIsPhysical &&
mri->getRegClass(srcReg) != mri->getRegClass(dstReg))
continue;
// If one is physical and one is virtual, check that the physical is
// allocatable in the class of the virtual.
if (srcRegIsPhysical && !dstRegIsPhysical) {
const TargetRegisterClass *dstRegClass = mri->getRegClass(dstReg);
if (std::find(dstRegClass->allocation_order_begin(*mf),
dstRegClass->allocation_order_end(*mf), srcReg) ==
dstRegClass->allocation_order_end(*mf))
continue;
}
if (!srcRegIsPhysical && dstRegIsPhysical) {
const TargetRegisterClass *srcRegClass = mri->getRegClass(srcReg);
if (std::find(srcRegClass->allocation_order_begin(*mf),
srcRegClass->allocation_order_end(*mf), dstReg) ==
srcRegClass->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 poorly defined def we err on the side of caution.
if (!(*vniItr)->def.isValid()) {
badDef = true;
break;
}
// 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)->getCopy() == instr)
continue;
if (!(*vniItr)->def.isValid()) {
badDef = true;
break;
}
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 = std::pow(10.0f, (float)loopInfo->getLoopDepth(mbb)) / 5.0;
coalescesFound[RegPair(srcReg, dstReg)] = cBenefit;
coalescesFound[RegPair(dstReg, srcReg)] = cBenefit;
}
}
return coalescesFound;
}
void RegAllocPBQP::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()) {
vregsToAlloc.insert(li->reg);
}
else {
emptyIntervalVRegs.insert(li->reg);
}
}
}
PBQP::Graph RegAllocPBQP::constructPBQPProblemOld() {
typedef std::vector<const LiveInterval*> LIVector;
typedef std::vector<unsigned> RegVector;
// 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 (RegSet::const_iterator itr = vregsToAlloc.begin(),
end = vregsToAlloc.end();
itr != end; ++itr) {
const LiveInterval *li = &lis->getInterval(*itr);
li2Node[li] = node2LI.size();
node2LI.push_back(li);
}
// Get the set of potential coalesces.
CoalesceMap coalesces;
if (pbqpCoalescing) {
coalesces = findCoalesces();
}
// Construct a PBQP solver for this problem
PBQP::Graph problem;
problemNodes.resize(vregsToAlloc.size());
// Resize allowedSets container appropriately.
allowedSets.resize(vregsToAlloc.size());
BitVector ReservedRegs = tri->getReservedRegs(*mf);
// 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;
TargetRegisterClass::iterator aob = liRC->allocation_order_begin(*mf);
TargetRegisterClass::iterator aoe = liRC->allocation_order_end(*mf);
for (TargetRegisterClass::iterator it = aob; it != aoe; ++it)
if (!ReservedRegs.test(*it))
liAllowed.push_back(*it);
// 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()) {
DEBUG(dbgs() << "CoalescingOverride: (" << li->reg << ", " << pReg << ")\n");
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;
}
}
}
assert(problem.getNumNodes() == allowedSets.size());
/*
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 RegAllocPBQP::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(
SlotIndex(), 0, false, lss->getVNInfoAllocator());
LiveInterval &rhsInterval = lis->getInterval(spilled->reg);
stackInterval.MergeRangesInAsValue(rhsInterval, vni);
}
bool RegAllocPBQP::mapPBQPToRegAllocOld(const PBQP::Solution &solution) {
// 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 (unsigned node = 0; node < node2LI.size(); ++node) {
unsigned virtReg = node2LI[node]->reg,
allocSelection = solution.getSelection(problemNodes[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];
DEBUG(dbgs() << "VREG " << virtReg << " -> "
<< tri->getName(physReg) << " (Option: " << allocSelection << ")\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
vregsToAlloc.erase(virtReg);
// Insert spill ranges for this live range
const LiveInterval *spillInterval = node2LI[node];
double oldSpillWeight = spillInterval->weight;
SmallVector<LiveInterval*, 8> spillIs;
rmf->rememberUseDefs(spillInterval);
std::vector<LiveInterval*> newSpills =
lis->addIntervalsForSpills(*spillInterval, spillIs, loopInfo, *vrm);
addStackInterval(spillInterval, mri);
rmf->rememberSpills(spillInterval, newSpills);
(void) oldSpillWeight;
DEBUG(dbgs() << "VREG " << virtReg << " -> SPILLED (Option: 0, 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.");
DEBUG(dbgs() << (*itr)->reg << " ");
vregsToAlloc.insert((*itr)->reg);
}
DEBUG(dbgs() << ")\n");
// We need another round if spill intervals were added.
anotherRoundNeeded |= !newSpills.empty();
}
}
return !anotherRoundNeeded;
}
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 " << vreg << " -> " << tri->getName(preg) << "\n");
assert(preg != 0 && "Invalid preg selected.");
vrm->assignVirt2Phys(vreg, preg);
} else if (problem.isSpillOption(vreg, alloc)) {
vregsToAlloc.erase(vreg);
const LiveInterval* spillInterval = &lis->getInterval(vreg);
double oldWeight = spillInterval->weight;
SmallVector<LiveInterval*, 8> spillIs;
rmf->rememberUseDefs(spillInterval);
std::vector<LiveInterval*> newSpills =
lis->addIntervalsForSpills(*spillInterval, spillIs, loopInfo, *vrm);
addStackInterval(spillInterval, mri);
rmf->rememberSpills(spillInterval, newSpills);
(void) oldWeight;
DEBUG(dbgs() << "VREG " << vreg << " -> SPILLED (Cost: "
<< oldWeight << ", 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.");
DEBUG(dbgs() << (*itr)->reg << " ");
vregsToAlloc.insert((*itr)->reg);
}
DEBUG(dbgs() << ")\n");
// We need another round if spill intervals were added.
anotherRoundNeeded |= !newSpills.empty();
} else {
assert(false && "Unknown allocation option.");
}
}
return !anotherRoundNeeded;
}
void RegAllocPBQP::finalizeAlloc() const {
typedef LiveIntervals::iterator LIIterator;
typedef LiveInterval::Ranges::const_iterator LRIterator;
// 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 = 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 RegAllocPBQP::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>();
rmf = &getAnalysis<RenderMachineFunction>();
vrm = &getAnalysis<VirtRegMap>();
DEBUG(dbgs() << "PBQP 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 are non-empty intervals allocate them using pbqp.
if (!vregsToAlloc.empty()) {
bool pbqpAllocComplete = false;
unsigned round = 0;
if (!pbqpBuilder) {
while (!pbqpAllocComplete) {
DEBUG(dbgs() << " PBQP Regalloc round " << round << ":\n");
PBQP::Graph problem = constructPBQPProblemOld();
PBQP::Solution solution =
PBQP::HeuristicSolver<PBQP::Heuristics::Briggs>::solve(problem);
pbqpAllocComplete = mapPBQPToRegAllocOld(solution);
++round;
}
} else {
while (!pbqpAllocComplete) {
DEBUG(dbgs() << " PBQP Regalloc round " << round << ":\n");
std::auto_ptr<PBQPRAProblem> problem =
builder->build(mf, lis, loopInfo, vregsToAlloc);
PBQP::Solution solution =
PBQP::HeuristicSolver<PBQP::Heuristics::Briggs>::solve(
problem->getGraph());
pbqpAllocComplete = mapPBQPToRegAlloc(*problem, solution);
++round;
}
}
}
// Finalise allocation, allocate empty ranges.
finalizeAlloc();
rmf->renderMachineFunction("After PBQP register allocation.", vrm);
vregsToAlloc.clear();
emptyIntervalVRegs.clear();
li2Node.clear();
node2LI.clear();
allowedSets.clear();
problemNodes.clear();
DEBUG(dbgs() << "Post alloc VirtRegMap:\n" << *vrm << "\n");
// Run rewriter
std::auto_ptr<VirtRegRewriter> rewriter(createVirtRegRewriter());
rewriter->runOnMachineFunction(*mf, *vrm, lis);
return true;
}
FunctionPass* llvm::createPBQPRegisterAllocator(
std::auto_ptr<PBQPBuilder> builder) {
return new RegAllocPBQP(builder);
}
FunctionPass* llvm::createDefaultPBQPRegisterAllocator() {
if (pbqpCoalescing) {
return createPBQPRegisterAllocator(
std::auto_ptr<PBQPBuilder>(new PBQPBuilderWithCoalescing()));
} // else
return createPBQPRegisterAllocator(
std::auto_ptr<PBQPBuilder>(new PBQPBuilder()));
}
#undef DEBUG_TYPE
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