C++ DomainValue类代码示例

DomainValue *ExeDepsFix::alloc(int domain) {
  DomainValue *dv = Avail.empty() ?
                      new(Allocator.Allocate()) DomainValue :
                      Avail.pop_back_val();
  if (domain >= 0)
    dv->addDomain(domain);
  assert(dv->Refs == 0 && "Reference count wasn't cleared");
  assert(!dv->Next && "Chained DomainValue shouldn't have been recycled");
  return dv;
}

// A soft instruction can be changed to work in other domains given by mask.
void ExeDepsFix::visitSoftInstr(MachineInstr *mi, unsigned mask) {
  // Bitmask of available domains for this instruction after taking collapsed
  // operands into account.
  unsigned available = mask;

  // Scan the explicit use operands for incoming domains.
  SmallVector<int, 4> used;
  if (LiveRegs)
    for (unsigned i = mi->getDesc().getNumDefs(),
                  e = mi->getDesc().getNumOperands(); i != e; ++i) {
      MachineOperand &mo = mi->getOperand(i);
      if (!mo.isReg()) continue;
      int rx = regIndex(mo.getReg());
      if (rx < 0) continue;
      if (DomainValue *dv = LiveRegs[rx].Value) {
        // Bitmask of domains that dv and available have in common.
        unsigned common = dv->getCommonDomains(available);
        // Is it possible to use this collapsed register for free?
        if (dv->isCollapsed()) {
          // Restrict available domains to the ones in common with the operand.
          // If there are no common domains, we must pay the cross-domain 
          // penalty for this operand.
          if (common) available = common;
        } else if (common)
          // Open DomainValue is compatible, save it for merging.
          used.push_back(rx);
        else
          // Open DomainValue is not compatible with instruction. It is useless
          // now.
          kill(rx);
      }
    }

  // If the collapsed operands force a single domain, propagate the collapse.
  if (isPowerOf2_32(available)) {
    unsigned domain = countTrailingZeros(available);
    TII->setExecutionDomain(mi, domain);
    visitHardInstr(mi, domain);
    return;
  }

  // Kill off any remaining uses that don't match available, and build a list of
  // incoming DomainValues that we want to merge.
  SmallVector<LiveReg, 4> Regs;
  for (SmallVector<int, 4>::iterator i=used.begin(), e=used.end(); i!=e; ++i) {
    int rx = *i;
    const LiveReg &LR = LiveRegs[rx];
    // This useless DomainValue could have been missed above.
    if (!LR.Value->getCommonDomains(available)) {
      kill(rx);
      continue;
    }
    // Sorted insertion.
    bool Inserted = false;
    for (SmallVector<LiveReg, 4>::iterator i = Regs.begin(), e = Regs.end();
           i != e && !Inserted; ++i) {
      if (LR.Def < i->Def) {
        Inserted = true;
        Regs.insert(i, LR);
      }
    }
    if (!Inserted)
      Regs.push_back(LR);
  }

  // doms are now sorted in order of appearance. Try to merge them all, giving
  // priority to the latest ones.
  DomainValue *dv = 0;
  while (!Regs.empty()) {
    if (!dv) {
      dv = Regs.pop_back_val().Value;
      // Force the first dv to match the current instruction.
      dv->AvailableDomains = dv->getCommonDomains(available);
      assert(dv->AvailableDomains && "Domain should have been filtered");
      continue;
    }

    DomainValue *Latest = Regs.pop_back_val().Value;
    // Skip already merged values.
    if (Latest == dv || Latest->Next)
      continue;
    if (merge(dv, Latest))
      continue;

    // If latest didn't merge, it is useless now. Kill all registers using it.
    for (SmallVector<int,4>::iterator i=used.begin(), e=used.end(); i != e; ++i)
      if (LiveRegs[*i].Value == Latest)
        kill(*i);
  }

  // dv is the DomainValue we are going to use for this instruction.
  if (!dv) {
    dv = alloc();
    dv->AvailableDomains = available;
  }
  dv->Instrs.push_back(mi);

  // Finally set all defs and non-collapsed uses to dv. We must iterate through
  // all the operators, including imp-def ones.
//.........这里部分代码省略.........

/// Set up LiveRegs by merging predecessor live-out values.
void ExeDepsFix::enterBasicBlock(MachineBasicBlock *MBB) {
  // Reset instruction counter in each basic block.
  CurInstr = 0;

  // Set up UndefReads to track undefined register reads.
  UndefReads.clear();
  LiveRegSet.clear();

  // Set up LiveRegs to represent registers entering MBB.
  if (!LiveRegs)
    LiveRegs = new LiveReg[NumRegs];

  // Default values are 'nothing happened a long time ago'.
  for (unsigned rx = 0; rx != NumRegs; ++rx) {
    LiveRegs[rx].Value = nullptr;
    LiveRegs[rx].Def = -(1 << 20);
  }

  // This is the entry block.
  if (MBB->pred_empty()) {
    for (const auto &LI : MBB->liveins()) {
      for (int rx : regIndices(LI.PhysReg)) {
        // Treat function live-ins as if they were defined just before the first
        // instruction.  Usually, function arguments are set up immediately
        // before the call.
        LiveRegs[rx].Def = -1;
      }
    }
    DEBUG(dbgs() << "BB#" << MBB->getNumber() << ": entry\n");
    return;
  }

  // Try to coalesce live-out registers from predecessors.
  for (MachineBasicBlock::const_pred_iterator pi = MBB->pred_begin(),
       pe = MBB->pred_end(); pi != pe; ++pi) {
    auto fi = MBBInfos.find(*pi);
    assert(fi != MBBInfos.end() &&
           "Should have pre-allocated MBBInfos for all MBBs");
    LiveReg *Incoming = fi->second.OutRegs;
    // Incoming is null if this is a backedge from a BB
    // we haven't processed yet
    if (Incoming == nullptr) {
      continue;
    }

    for (unsigned rx = 0; rx != NumRegs; ++rx) {
      // Use the most recent predecessor def for each register.
      LiveRegs[rx].Def = std::max(LiveRegs[rx].Def, Incoming[rx].Def);

      DomainValue *pdv = resolve(Incoming[rx].Value);
      if (!pdv)
        continue;
      if (!LiveRegs[rx].Value) {
        setLiveReg(rx, pdv);
        continue;
      }

      // We have a live DomainValue from more than one predecessor.
      if (LiveRegs[rx].Value->isCollapsed()) {
        // We are already collapsed, but predecessor is not. Force it.
        unsigned Domain = LiveRegs[rx].Value->getFirstDomain();
        if (!pdv->isCollapsed() && pdv->hasDomain(Domain))
          collapse(pdv, Domain);
        continue;
      }

      // Currently open, merge in predecessor.
      if (!pdv->isCollapsed())
        merge(LiveRegs[rx].Value, pdv);
      else
        force(rx, pdv->getFirstDomain());
    }
  }
  DEBUG(
      dbgs() << "BB#" << MBB->getNumber()
             << (!isBlockDone(MBB) ? ": incomplete\n" : ": all preds known\n"));
}