C++ SmallSetVector::pop_back_val方法代码示例

/// propagateSiblingValue - Propagate the value in SVI to dependents if it is
/// known.  Otherwise remember the dependency for later.
///
/// @param SVIIter SibValues entry to propagate.
/// @param VNI Dependent value, or NULL to propagate to all saved dependents.
void InlineSpiller::propagateSiblingValue(SibValueMap::iterator SVIIter,
                                          VNInfo *VNI) {
  SibValueMap::value_type *SVI = &*SVIIter;

  // When VNI is non-NULL, add it to SVI's deps, and only propagate to that.
  TinyPtrVector<VNInfo*> FirstDeps;
  if (VNI) {
    FirstDeps.push_back(VNI);
    SVI->second.Deps.push_back(VNI);
  }

  // Has the value been completely determined yet?  If not, defer propagation.
  if (!SVI->second.hasDef())
    return;

  // Work list of values to propagate.
  SmallSetVector<SibValueMap::value_type *, 8> WorkList;
  WorkList.insert(SVI);

  do {
    SVI = WorkList.pop_back_val();
    TinyPtrVector<VNInfo*> *Deps = VNI ? &FirstDeps : &SVI->second.Deps;
    VNI = 0;

    SibValueInfo &SV = SVI->second;
    if (!SV.SpillMBB)
      SV.SpillMBB = LIS.getMBBFromIndex(SV.SpillVNI->def);

    DEBUG(dbgs() << "  prop to " << Deps->size() << ": "
                 << SVI->first->id << '@' << SVI->first->def << ":\t" << SV);

    assert(SV.hasDef() && "Propagating undefined value");

    // Should this value be propagated as a preferred spill candidate?  We don't
    // propagate values of registers that are about to spill.
    bool PropSpill = !DisableHoisting && !isRegToSpill(SV.SpillReg);
    unsigned SpillDepth = ~0u;

    for (TinyPtrVector<VNInfo*>::iterator DepI = Deps->begin(),
         DepE = Deps->end(); DepI != DepE; ++DepI) {
      SibValueMap::iterator DepSVI = SibValues.find(*DepI);
      assert(DepSVI != SibValues.end() && "Dependent value not in SibValues");
      SibValueInfo &DepSV = DepSVI->second;
      if (!DepSV.SpillMBB)
        DepSV.SpillMBB = LIS.getMBBFromIndex(DepSV.SpillVNI->def);

      bool Changed = false;

      // Propagate defining instruction.
      if (!DepSV.hasDef()) {
        Changed = true;
        DepSV.DefMI = SV.DefMI;
        DepSV.DefByOrigPHI = SV.DefByOrigPHI;
      }

      // Propagate AllDefsAreReloads.  For PHI values, this computes an AND of
      // all predecessors.
      if (!SV.AllDefsAreReloads && DepSV.AllDefsAreReloads) {
        Changed = true;
        DepSV.AllDefsAreReloads = false;
      }

      // Propagate best spill value.
      if (PropSpill && SV.SpillVNI != DepSV.SpillVNI) {
        if (SV.SpillMBB == DepSV.SpillMBB) {
          // DepSV is in the same block.  Hoist when dominated.
          if (DepSV.KillsSource && SV.SpillVNI->def < DepSV.SpillVNI->def) {
            // This is an alternative def earlier in the same MBB.
            // Hoist the spill as far as possible in SpillMBB. This can ease
            // register pressure:
            //
            //   x = def
            //   y = use x
            //   s = copy x
            //
            // Hoisting the spill of s to immediately after the def removes the
            // interference between x and y:
            //
            //   x = def
            //   spill x
            //   y = use x<kill>
            //
            // This hoist only helps when the DepSV copy kills its source.
            Changed = true;
            DepSV.SpillReg = SV.SpillReg;
            DepSV.SpillVNI = SV.SpillVNI;
            DepSV.SpillMBB = SV.SpillMBB;
          }
        } else {
          // DepSV is in a different block.
          if (SpillDepth == ~0u)
            SpillDepth = Loops.getLoopDepth(SV.SpillMBB);

          // Also hoist spills to blocks with smaller loop depth, but make sure
          // that the new value dominates.  Non-phi dependents are always
//.........这里部分代码省略.........

/// \brief Figure out if the loop is worth full unrolling.
///
/// Complete loop unrolling can make some loads constant, and we need to know
/// if that would expose any further optimization opportunities.  This routine
/// estimates this optimization.  It computes cost of unrolled loop
/// (UnrolledCost) and dynamic cost of the original loop (RolledDynamicCost). By
/// dynamic cost we mean that we won't count costs of blocks that are known not
/// to be executed (i.e. if we have a branch in the loop and we know that at the
/// given iteration its condition would be resolved to true, we won't add up the
/// cost of the 'false'-block).
/// \returns Optional value, holding the RolledDynamicCost and UnrolledCost. If
/// the analysis failed (no benefits expected from the unrolling, or the loop is
/// too big to analyze), the returned value is None.
static Optional<EstimatedUnrollCost>
analyzeLoopUnrollCost(const Loop *L, unsigned TripCount, DominatorTree &DT,
                      ScalarEvolution &SE, const TargetTransformInfo &TTI,
                      int MaxUnrolledLoopSize) {
  // We want to be able to scale offsets by the trip count and add more offsets
  // to them without checking for overflows, and we already don't want to
  // analyze *massive* trip counts, so we force the max to be reasonably small.
  assert(UnrollMaxIterationsCountToAnalyze < (INT_MAX / 2) &&
         "The unroll iterations max is too large!");

  // Only analyze inner loops. We can't properly estimate cost of nested loops
  // and we won't visit inner loops again anyway.
  if (!L->empty())
    return None;

  // Don't simulate loops with a big or unknown tripcount
  if (!UnrollMaxIterationsCountToAnalyze || !TripCount ||
      TripCount > UnrollMaxIterationsCountToAnalyze)
    return None;

  SmallSetVector<BasicBlock *, 16> BBWorklist;
  SmallSetVector<std::pair<BasicBlock *, BasicBlock *>, 4> ExitWorklist;
  DenseMap<Value *, Constant *> SimplifiedValues;
  SmallVector<std::pair<Value *, Constant *>, 4> SimplifiedInputValues;

  // The estimated cost of the unrolled form of the loop. We try to estimate
  // this by simplifying as much as we can while computing the estimate.
  int UnrolledCost = 0;

  // We also track the estimated dynamic (that is, actually executed) cost in
  // the rolled form. This helps identify cases when the savings from unrolling
  // aren't just exposing dead control flows, but actual reduced dynamic
  // instructions due to the simplifications which we expect to occur after
  // unrolling.
  int RolledDynamicCost = 0;

  // We track the simplification of each instruction in each iteration. We use
  // this to recursively merge costs into the unrolled cost on-demand so that
  // we don't count the cost of any dead code. This is essentially a map from
  // <instruction, int> to <bool, bool>, but stored as a densely packed struct.
  DenseSet<UnrolledInstState, UnrolledInstStateKeyInfo> InstCostMap;

  // A small worklist used to accumulate cost of instructions from each
  // observable and reached root in the loop.
  SmallVector<Instruction *, 16> CostWorklist;

  // PHI-used worklist used between iterations while accumulating cost.
  SmallVector<Instruction *, 4> PHIUsedList;

  // Helper function to accumulate cost for instructions in the loop.
  auto AddCostRecursively = [&](Instruction &RootI, int Iteration) {
    assert(Iteration >= 0 && "Cannot have a negative iteration!");
    assert(CostWorklist.empty() && "Must start with an empty cost list");
    assert(PHIUsedList.empty() && "Must start with an empty phi used list");
    CostWorklist.push_back(&RootI);
    for (;; --Iteration) {
      do {
        Instruction *I = CostWorklist.pop_back_val();

        // InstCostMap only uses I and Iteration as a key, the other two values
        // don't matter here.
        auto CostIter = InstCostMap.find({I, Iteration, 0, 0});
        if (CostIter == InstCostMap.end())
          // If an input to a PHI node comes from a dead path through the loop
          // we may have no cost data for it here. What that actually means is
          // that it is free.
          continue;
        auto &Cost = *CostIter;
        if (Cost.IsCounted)
          // Already counted this instruction.
          continue;

        // Mark that we are counting the cost of this instruction now.
        Cost.IsCounted = true;

        // If this is a PHI node in the loop header, just add it to the PHI set.
        if (auto *PhiI = dyn_cast<PHINode>(I))
          if (PhiI->getParent() == L->getHeader()) {
            assert(Cost.IsFree && "Loop PHIs shouldn't be evaluated as they "
                                  "inherently simplify during unrolling.");
            if (Iteration == 0)
              continue;

            // Push the incoming value from the backedge into the PHI used list
            // if it is an in-loop instruction. We'll use this to populate the
            // cost worklist for the next iteration (as we count backwards).
            if (auto *OpI = dyn_cast<Instruction>(
//.........这里部分代码省略.........

//.........这里部分代码省略.........
    for (MachineBasicBlock *Succ : MBB->successors()) {
      // Ignore backedges.
      if (MachineLoop *SuccL = MLI.getLoopFor(Succ))
        if (SuccL->getHeader() == Succ && SuccL->contains(MBB))
          continue;
      // Decrement the predecessor count. If it's now zero, it's ready.
      if (--NumPredsLeft[Succ->getNumber()] == 0)
        Preferred.push(Succ);
    }
    // Determine the block to follow MBB. First try to find a preferred block,
    // to preserve the original block order when possible.
    MachineBasicBlock *Next = nullptr;
    while (!Preferred.empty()) {
      Next = Preferred.top();
      Preferred.pop();
      // If X isn't dominated by the top active loop header, defer it until that
      // loop is done.
      if (!Loops.empty() &&
          !MDT.dominates(Loops.back().Loop->getHeader(), Next)) {
        Loops.back().Deferred.push_back(Next);
        Next = nullptr;
        continue;
      }
      // If Next was originally ordered before MBB, and it isn't because it was
      // loop-rotated above the header, it's not preferred.
      if (Next->getNumber() < MBB->getNumber() &&
          (!L || !L->contains(Next) ||
           L->getHeader()->getNumber() < Next->getNumber())) {
        Ready.push(Next);
        Next = nullptr;
        continue;
      }
      break;
    }
    // If we didn't find a suitable block in the Preferred list, check the
    // general Ready list.
    if (!Next) {
      // If there are no more blocks to process, we're done.
      if (Ready.empty()) {
        MaybeUpdateTerminator(MBB);
        break;
      }
      for (;;) {
        Next = Ready.top();
        Ready.pop();
        // If Next isn't dominated by the top active loop header, defer it until
        // that loop is done.
        if (!Loops.empty() &&
            !MDT.dominates(Loops.back().Loop->getHeader(), Next)) {
          Loops.back().Deferred.push_back(Next);
          continue;
        }
        break;
      }
    }
    // Move the next block into place and iterate.
    Next->moveAfter(MBB);
    MaybeUpdateTerminator(MBB);
    MBB = Next;
  }
  assert(Loops.empty() && "Active loop list not finished");
  MF.RenumberBlocks();

#ifndef NDEBUG
  SmallSetVector<MachineLoop *, 8> OnStack;

  // Insert a sentinel representing the degenerate loop that starts at the
  // function entry block and includes the entire function as a "loop" that
  // executes once.
  OnStack.insert(nullptr);

  for (auto &MBB : MF) {
    assert(MBB.getNumber() >= 0 && "Renumbered blocks should be non-negative.");

    MachineLoop *Loop = MLI.getLoopFor(&MBB);
    if (Loop && &MBB == Loop->getHeader()) {
      // Loop header. The loop predecessor should be sorted above, and the other
      // predecessors should be backedges below.
      for (auto Pred : MBB.predecessors())
        assert(
            (Pred->getNumber() < MBB.getNumber() || Loop->contains(Pred)) &&
            "Loop header predecessors must be loop predecessors or backedges");
      assert(OnStack.insert(Loop) && "Loops should be declared at most once.");
    } else {
      // Not a loop header. All predecessors should be sorted above.
      for (auto Pred : MBB.predecessors())
        assert(Pred->getNumber() < MBB.getNumber() &&
               "Non-loop-header predecessors should be topologically sorted");
      assert(OnStack.count(MLI.getLoopFor(&MBB)) &&
             "Blocks must be nested in their loops");
    }
    while (OnStack.size() > 1 && &MBB == LoopBottom(OnStack.back()))
      OnStack.pop_back();
  }
  assert(OnStack.pop_back_val() == nullptr &&
         "The function entry block shouldn't actually be a loop header");
  assert(OnStack.empty() &&
         "Control flow stack pushes and pops should be balanced.");
#endif
}

/// Sort the blocks in RPO, taking special care to make sure that loops are
/// contiguous even in the case of split backedges.
///
/// TODO: Determine whether RPO is actually worthwhile, or whether we should
/// move to just a stable-topological-sort-based approach that would preserve
/// more of the original order.
static void SortBlocks(MachineFunction &MF, const MachineLoopInfo &MLI) {
  // Note that we do our own RPO rather than using
  // "llvm/ADT/PostOrderIterator.h" because we want control over the order that
  // successors are visited in (see above). Also, we can sort the blocks in the
  // MachineFunction as we go.
  SmallPtrSet<MachineBasicBlock *, 16> Visited;
  SmallVector<POStackEntry, 16> Stack;

  MachineBasicBlock *EntryBlock = &*MF.begin();
  Visited.insert(EntryBlock);
  Stack.push_back(POStackEntry(EntryBlock, MF, MLI));

  for (;;) {
    POStackEntry &Entry = Stack.back();
    SmallVectorImpl<MachineBasicBlock *> &Succs = Entry.Succs;
    if (!Succs.empty()) {
      MachineBasicBlock *Succ = Succs.pop_back_val();
      if (Visited.insert(Succ).second)
        Stack.push_back(POStackEntry(Succ, MF, MLI));
      continue;
    }

    // Put the block in its position in the MachineFunction.
    MachineBasicBlock &MBB = *Entry.MBB;
    MBB.moveBefore(&*MF.begin());

    // Branch instructions may utilize a fallthrough, so update them if a
    // fallthrough has been added or removed.
    if (!MBB.empty() && MBB.back().isTerminator() && !MBB.back().isBranch() &&
        !MBB.back().isBarrier())
      report_fatal_error(
          "Non-branch terminator with fallthrough cannot yet be rewritten");
    if (MBB.empty() || !MBB.back().isTerminator() || MBB.back().isBranch())
      MBB.updateTerminator();

    Stack.pop_back();
    if (Stack.empty())
      break;
  }

  // Now that we've sorted the blocks in RPO, renumber them.
  MF.RenumberBlocks();

#ifndef NDEBUG
  SmallSetVector<MachineLoop *, 8> OnStack;

  // Insert a sentinel representing the degenerate loop that starts at the
  // function entry block and includes the entire function as a "loop" that
  // executes once.
  OnStack.insert(nullptr);

  for (auto &MBB : MF) {
    assert(MBB.getNumber() >= 0 && "Renumbered blocks should be non-negative.");

    MachineLoop *Loop = MLI.getLoopFor(&MBB);
    if (Loop && &MBB == Loop->getHeader()) {
      // Loop header. The loop predecessor should be sorted above, and the other
      // predecessors should be backedges below.
      for (auto Pred : MBB.predecessors())
        assert(
            (Pred->getNumber() < MBB.getNumber() || Loop->contains(Pred)) &&
            "Loop header predecessors must be loop predecessors or backedges");
      assert(OnStack.insert(Loop) && "Loops should be declared at most once.");
    } else {
      // Not a loop header. All predecessors should be sorted above.
      for (auto Pred : MBB.predecessors())
        assert(Pred->getNumber() < MBB.getNumber() &&
               "Non-loop-header predecessors should be topologically sorted");
      assert(OnStack.count(MLI.getLoopFor(&MBB)) &&
             "Blocks must be nested in their loops");
    }
    while (OnStack.size() > 1 && &MBB == LoopBottom(OnStack.back()))
      OnStack.pop_back();
  }
  assert(OnStack.pop_back_val() == nullptr &&
         "The function entry block shouldn't actually be a loop header");
  assert(OnStack.empty() &&
         "Control flow stack pushes and pops should be balanced.");
#endif
}