LiveRegMatrix.cpp

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//===-- LiveRegMatrix.cpp - Track register interference -------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the LiveRegMatrix analysis pass.
//
//===----------------------------------------------------------------------===//

#include "llvm/CodeGen/LiveRegMatrix.h"
#include "RegisterCoalescer.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/VirtRegMap.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetRegisterInfo.h"

using namespace llvm;

#define DEBUG_TYPE "regalloc"

STATISTIC(NumAssigned   , "Number of registers assigned");
STATISTIC(NumUnassigned , "Number of registers unassigned");

char LiveRegMatrix::ID = 0;
INITIALIZE_PASS_BEGIN(LiveRegMatrix, "liveregmatrix",
                      "Live Register Matrix", false, false)
INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
INITIALIZE_PASS_DEPENDENCY(VirtRegMap)
INITIALIZE_PASS_END(LiveRegMatrix, "liveregmatrix",
                    "Live Register Matrix", false, false)

LiveRegMatrix::LiveRegMatrix() : MachineFunctionPass(ID),
  UserTag(0), RegMaskTag(0), RegMaskVirtReg(0) {}

void LiveRegMatrix::getAnalysisUsage(AnalysisUsage &AU) const {
  AU.setPreservesAll();
  AU.addRequiredTransitive<LiveIntervals>();
  AU.addRequiredTransitive<VirtRegMap>();
  MachineFunctionPass::getAnalysisUsage(AU);
}

bool LiveRegMatrix::runOnMachineFunction(MachineFunction &MF) {
  TRI = MF.getSubtarget().getRegisterInfo();
  MRI = &MF.getRegInfo();
  LIS = &getAnalysis<LiveIntervals>();
  VRM = &getAnalysis<VirtRegMap>();

  unsigned NumRegUnits = TRI->getNumRegUnits();
  if (NumRegUnits != Matrix.size())
    Queries.reset(new LiveIntervalUnion::Query[NumRegUnits]);
  Matrix.init(LIUAlloc, NumRegUnits);

  // Make sure no stale queries get reused.
  invalidateVirtRegs();
  return false;
}

void LiveRegMatrix::releaseMemory() {
  for (unsigned i = 0, e = Matrix.size(); i != e; ++i) {
    Matrix[i].clear();
    // No need to clear Queries here, since LiveIntervalUnion::Query doesn't
    // have anything important to clear and LiveRegMatrix's runOnFunction()
    // does a std::unique_ptr::reset anyways.
  }
}

void LiveRegMatrix::assign(LiveInterval &VirtReg, unsigned PhysReg) {
  DEBUG(dbgs() << "assigning " << PrintReg(VirtReg.reg, TRI)
               << " to " << PrintReg(PhysReg, TRI) << ':');
  assert(!VRM->hasPhys(VirtReg.reg) && "Duplicate VirtReg assignment");
  VRM->assignVirt2Phys(VirtReg.reg, PhysReg);
  MRI->setPhysRegUsed(PhysReg);
  for (MCRegUnitIterator Units(PhysReg, TRI); Units.isValid(); ++Units) {
    DEBUG(dbgs() << ' ' << PrintRegUnit(*Units, TRI));
    Matrix[*Units].unify(VirtReg);
  }
  ++NumAssigned;
  DEBUG(dbgs() << '\n');
}

void LiveRegMatrix::unassign(LiveInterval &VirtReg) {
  unsigned PhysReg = VRM->getPhys(VirtReg.reg);
  DEBUG(dbgs() << "unassigning " << PrintReg(VirtReg.reg, TRI)
               << " from " << PrintReg(PhysReg, TRI) << ':');
  VRM->clearVirt(VirtReg.reg);
  for (MCRegUnitIterator Units(PhysReg, TRI); Units.isValid(); ++Units) {
    DEBUG(dbgs() << ' ' << PrintRegUnit(*Units, TRI));
    Matrix[*Units].extract(VirtReg);
  }
  ++NumUnassigned;
  DEBUG(dbgs() << '\n');
}

bool LiveRegMatrix::checkRegMaskInterference(LiveInterval &VirtReg,
                                             unsigned PhysReg) {
  // Check if the cached information is valid.
  // The same BitVector can be reused for all PhysRegs.
  // We could cache multiple VirtRegs if it becomes necessary.
  if (RegMaskVirtReg != VirtReg.reg || RegMaskTag != UserTag) {
    RegMaskVirtReg = VirtReg.reg;
    RegMaskTag = UserTag;
    RegMaskUsable.clear();
    LIS->checkRegMaskInterference(VirtReg, RegMaskUsable);
  }

  // The BitVector is indexed by PhysReg, not register unit.
  // Regmask interference is more fine grained than regunits.
  // For example, a Win64 call can clobber %ymm8 yet preserve %xmm8.
  return !RegMaskUsable.empty() && (!PhysReg || !RegMaskUsable.test(PhysReg));
}

bool LiveRegMatrix::checkRegUnitInterference(LiveInterval &VirtReg,
                                             unsigned PhysReg) {
  if (VirtReg.empty())
    return false;
  CoalescerPair CP(VirtReg.reg, PhysReg, *TRI);
  for (MCRegUnitIterator Units(PhysReg, TRI); Units.isValid(); ++Units) {
    const LiveRange &UnitRange = LIS->getRegUnit(*Units);
    if (VirtReg.overlaps(UnitRange, CP, *LIS->getSlotIndexes()))
      return true;
  }
  return false;
}

LiveIntervalUnion::Query &LiveRegMatrix::query(LiveInterval &VirtReg,
                                               unsigned RegUnit) {
  LiveIntervalUnion::Query &Q = Queries[RegUnit];
  Q.init(UserTag, &VirtReg, &Matrix[RegUnit]);
  return Q;
}

LiveRegMatrix::InterferenceKind
LiveRegMatrix::checkInterference(LiveInterval &VirtReg, unsigned PhysReg) {
  if (VirtReg.empty())
    return IK_Free;

  // Regmask interference is the fastest check.
  if (checkRegMaskInterference(VirtReg, PhysReg))
    return IK_RegMask;

  // Check for fixed interference.
  if (checkRegUnitInterference(VirtReg, PhysReg))
    return IK_RegUnit;

  // Check the matrix for virtual register interference.
  for (MCRegUnitIterator Units(PhysReg, TRI); Units.isValid(); ++Units)
    if (query(VirtReg, *Units).checkInterference())
      return IK_VirtReg;

  return IK_Free;
}