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

    // following functions are shamelessly copied from LLVM.
    bool isPotentiallyReachableFromMany(SmallVectorImpl<BasicBlock *> &Worklist, BasicBlock *StopBB) {

        // Limit the number of blocks we visit. The goal is to avoid run-away compile
        // times on large CFGs without hampering sensible code. Arbitrarily chosen.
        unsigned Limit = 32;
        SmallSet<const BasicBlock*, 64> Visited;
        do {
            BasicBlock *BB = Worklist.pop_back_val();
            if (!Visited.insert(BB).second)
                continue;
            if (BB == StopBB)
                return true;

            if (!--Limit) {
                // We haven't been able to prove it one way or the other. Conservatively
                // answer true -- that there is potentially a path.
                return true;
            }
            Worklist.append(succ_begin(BB), succ_end(BB));
        } while (!Worklist.empty());

        // We have exhausted all possible paths and are certain that 'To' can not be
        // reached from 'From'.
        return false;
    }

/// Emit a check for whether a non-native function call produced an
/// error.
///
/// \c results should be left with only values that match the formal
/// direct results of the function.
void
SILGenFunction::emitForeignErrorCheck(SILLocation loc,
                                      SmallVectorImpl<ManagedValue> &results,
                                      ManagedValue errorSlot,
                                      bool suppressErrorCheck,
                                const ForeignErrorConvention &foreignError) {
  // All of this is autogenerated.
  loc.markAutoGenerated();

  switch (foreignError.getKind()) {
  case ForeignErrorConvention::ZeroPreservedResult:
    assert(results.size() == 1);
    emitResultIsZeroErrorCheck(*this, loc, results[0], errorSlot,
                               suppressErrorCheck,
                               /*zeroIsError*/ true);
    return;
  case ForeignErrorConvention::ZeroResult:
    assert(results.size() == 1);
    emitResultIsZeroErrorCheck(*this, loc, results.pop_back_val(),
                               errorSlot, suppressErrorCheck,
                               /*zeroIsError*/ true);
    return;
  case ForeignErrorConvention::NonZeroResult:
    assert(results.size() == 1);
    emitResultIsZeroErrorCheck(*this, loc, results.pop_back_val(),
                               errorSlot, suppressErrorCheck,
                               /*zeroIsError*/ false);
    return;
  case ForeignErrorConvention::NilResult:
    assert(results.size() == 1);
    results[0] = emitResultIsNilErrorCheck(*this, loc, results[0], errorSlot,
                                           suppressErrorCheck);
    return;
  case ForeignErrorConvention::NonNilError:
    // Leave the direct results alone.
    emitErrorIsNonNilErrorCheck(*this, loc, errorSlot, suppressErrorCheck);
    return;
  }
  llvm_unreachable("bad foreign error convention kind");
}

/// \brief Given a list of combinable load. Combine the maximum number of them.
bool LoadCombine::combineLoads(SmallVectorImpl<LoadPOPPair> &Loads) {
  // Remove loads from the end while the size is not a power of 2.
  unsigned TotalSize = 0;
  for (const auto &L : Loads)
    TotalSize += L.Load->getType()->getPrimitiveSizeInBits();
  while (TotalSize != 0 && !isPowerOf2_32(TotalSize))
    TotalSize -= Loads.pop_back_val().Load->getType()->getPrimitiveSizeInBits();
  if (Loads.size() < 2)
    return false;

  DEBUG({
    dbgs() << "***** Combining Loads ******\n";
    for (const auto &L : Loads) {
      dbgs() << L.POP.Offset << ": " << *L.Load << "\n";
    }
  });

static bool isPotentiallyReachableInner(SmallVectorImpl<BasicBlock *> &Worklist,
                                        BasicBlock *StopBB,
                                        const DominatorTree *DT,
                                        const LoopInfo *LI) {
  // When the stop block is unreachable, it's dominated from everywhere,
  // regardless of whether there's a path between the two blocks.
  if (DT && !DT->isReachableFromEntry(StopBB))
    DT = 0;

  // Limit the number of blocks we visit. The goal is to avoid run-away compile
  // times on large CFGs without hampering sensible code. Arbitrarily chosen.
  unsigned Limit = 32;
  SmallSet<const BasicBlock*, 64> Visited;
  do {
    BasicBlock *BB = Worklist.pop_back_val();
    if (!Visited.insert(BB))
      continue;
    if (BB == StopBB)
      return true;
    if (DT && DT->dominates(BB, StopBB))
      return true;
    if (LI && loopContainsBoth(LI, BB, StopBB))
      return true;

    if (!--Limit) {
      // We haven't been able to prove it one way or the other. Conservatively
      // answer true -- that there is potentially a path.
      return true;
    }

    if (const Loop *Outer = LI ? getOutermostLoop(LI, BB) : 0) {
      // All blocks in a single loop are reachable from all other blocks. From
      // any of these blocks, we can skip directly to the exits of the loop,
      // ignoring any other blocks inside the loop body.
      Outer->getExitBlocks(Worklist);
    } else {
      for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
        Worklist.push_back(*I);
    }
  } while (!Worklist.empty());

  // We have exhausted all possible paths and are certain that 'To' can not be
  // reached from 'From'.
  return false;
}

/// For every instruction from the worklist, check to see if it has any uses
/// that are outside the current loop.  If so, insert LCSSA PHI nodes and
/// rewrite the uses.
bool llvm::formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist,
                                    DominatorTree &DT, LoopInfo &LI) {
    SmallVector<Use *, 16> UsesToRewrite;
    SmallSetVector<PHINode *, 16> PHIsToRemove;
    PredIteratorCache PredCache;
    bool Changed = false;

    // Cache the Loop ExitBlocks across this loop.  We expect to get a lot of
    // instructions within the same loops, computing the exit blocks is
    // expensive, and we're not mutating the loop structure.
    SmallDenseMap<Loop*, SmallVector<BasicBlock *,1>> LoopExitBlocks;

    while (!Worklist.empty()) {
        UsesToRewrite.clear();

        Instruction *I = Worklist.pop_back_val();
        BasicBlock *InstBB = I->getParent();
        Loop *L = LI.getLoopFor(InstBB);
        if (!LoopExitBlocks.count(L))
            L->getExitBlocks(LoopExitBlocks[L]);
        assert(LoopExitBlocks.count(L));
        const SmallVectorImpl<BasicBlock *> &ExitBlocks = LoopExitBlocks[L];

        if (ExitBlocks.empty())
            continue;

        // Tokens cannot be used in PHI nodes, so we skip over them.
        // We can run into tokens which are live out of a loop with catchswitch
        // instructions in Windows EH if the catchswitch has one catchpad which
        // is inside the loop and another which is not.
        if (I->getType()->isTokenTy())
            continue;

        for (Use &U : I->uses()) {
            Instruction *User = cast<Instruction>(U.getUser());
            BasicBlock *UserBB = User->getParent();
            if (PHINode *PN = dyn_cast<PHINode>(User))
                UserBB = PN->getIncomingBlock(U);

            if (InstBB != UserBB && !L->contains(UserBB))
                UsesToRewrite.push_back(&U);
        }

        // If there are no uses outside the loop, exit with no change.
        if (UsesToRewrite.empty())
            continue;

        ++NumLCSSA; // We are applying the transformation

        // Invoke instructions are special in that their result value is not
        // available along their unwind edge. The code below tests to see whether
        // DomBB dominates the value, so adjust DomBB to the normal destination
        // block, which is effectively where the value is first usable.
        BasicBlock *DomBB = InstBB;
        if (InvokeInst *Inv = dyn_cast<InvokeInst>(I))
            DomBB = Inv->getNormalDest();

        DomTreeNode *DomNode = DT.getNode(DomBB);

        SmallVector<PHINode *, 16> AddedPHIs;
        SmallVector<PHINode *, 8> PostProcessPHIs;

        SmallVector<PHINode *, 4> InsertedPHIs;
        SSAUpdater SSAUpdate(&InsertedPHIs);
        SSAUpdate.Initialize(I->getType(), I->getName());

        // Insert the LCSSA phi's into all of the exit blocks dominated by the
        // value, and add them to the Phi's map.
        for (BasicBlock *ExitBB : ExitBlocks) {
            if (!DT.dominates(DomNode, DT.getNode(ExitBB)))
                continue;

            // If we already inserted something for this BB, don't reprocess it.
            if (SSAUpdate.HasValueForBlock(ExitBB))
                continue;

            PHINode *PN = PHINode::Create(I->getType(), PredCache.size(ExitBB),
                                          I->getName() + ".lcssa", &ExitBB->front());

            // Add inputs from inside the loop for this PHI.
            for (BasicBlock *Pred : PredCache.get(ExitBB)) {
                PN->addIncoming(I, Pred);

                // If the exit block has a predecessor not within the loop, arrange for
                // the incoming value use corresponding to that predecessor to be
                // rewritten in terms of a different LCSSA PHI.
                if (!L->contains(Pred))
                    UsesToRewrite.push_back(
                        &PN->getOperandUse(PN->getOperandNumForIncomingValue(
                                               PN->getNumIncomingValues() - 1)));
            }

            AddedPHIs.push_back(PN);

            // Remember that this phi makes the value alive in this block.
            SSAUpdate.AddAvailableValue(ExitBB, PN);

//.........这里部分代码省略.........

bool llvm::isPotentiallyReachableFromMany(
    SmallVectorImpl<BasicBlock *> &Worklist, BasicBlock *StopBB,
    const SmallPtrSetImpl<BasicBlock *> *ExclusionSet, const DominatorTree *DT,
    const LoopInfo *LI) {
  // When the stop block is unreachable, it's dominated from everywhere,
  // regardless of whether there's a path between the two blocks.
  if (DT && !DT->isReachableFromEntry(StopBB))
    DT = nullptr;

  // We can't skip directly from a block that dominates the stop block if the
  // exclusion block is potentially in between.
  if (ExclusionSet && !ExclusionSet->empty())
    DT = nullptr;

  // Normally any block in a loop is reachable from any other block in a loop,
  // however excluded blocks might partition the body of a loop to make that
  // untrue.
  SmallPtrSet<const Loop *, 8> LoopsWithHoles;
  if (LI && ExclusionSet) {
    for (auto BB : *ExclusionSet) {
      if (const Loop *L = getOutermostLoop(LI, BB))
        LoopsWithHoles.insert(L);
    }
  }

  const Loop *StopLoop = LI ? getOutermostLoop(LI, StopBB) : nullptr;

  // Limit the number of blocks we visit. The goal is to avoid run-away compile
  // times on large CFGs without hampering sensible code. Arbitrarily chosen.
  unsigned Limit = 32;
  SmallPtrSet<const BasicBlock*, 32> Visited;
  do {
    BasicBlock *BB = Worklist.pop_back_val();
    if (!Visited.insert(BB).second)
      continue;
    if (BB == StopBB)
      return true;
    if (ExclusionSet && ExclusionSet->count(BB))
      continue;
    if (DT && DT->dominates(BB, StopBB))
      return true;

    const Loop *Outer = nullptr;
    if (LI) {
      Outer = getOutermostLoop(LI, BB);
      // If we're in a loop with a hole, not all blocks in the loop are
      // reachable from all other blocks. That implies we can't simply jump to
      // the loop's exit blocks, as that exit might need to pass through an
      // excluded block. Clear Outer so we process BB's successors.
      if (LoopsWithHoles.count(Outer))
        Outer = nullptr;
      if (StopLoop && Outer == StopLoop)
        return true;
    }

    if (!--Limit) {
      // We haven't been able to prove it one way or the other. Conservatively
      // answer true -- that there is potentially a path.
      return true;
    }

    if (Outer) {
      // All blocks in a single loop are reachable from all other blocks. From
      // any of these blocks, we can skip directly to the exits of the loop,
      // ignoring any other blocks inside the loop body.
      Outer->getExitBlocks(Worklist);
    } else {
      Worklist.append(succ_begin(BB), succ_end(BB));
    }
  } while (!Worklist.empty());

  // We have exhausted all possible paths and are certain that 'To' can not be
  // reached from 'From'.
  return false;
}

void LiveRangeEdit::eliminateDeadDefs(SmallVectorImpl<MachineInstr*> &Dead,
                                      ArrayRef<unsigned> RegsBeingSpilled) {
  ToShrinkSet ToShrink;

  for (;;) {
    // Erase all dead defs.
    while (!Dead.empty())
      eliminateDeadDef(Dead.pop_back_val(), ToShrink);

    if (ToShrink.empty())
      break;

    // Shrink just one live interval. Then delete new dead defs.
    LiveInterval *LI = ToShrink.back();
    ToShrink.pop_back();
    if (foldAsLoad(LI, Dead))
      continue;
    if (TheDelegate)
      TheDelegate->LRE_WillShrinkVirtReg(LI->reg);
    if (!LIS.shrinkToUses(LI, &Dead))
      continue;

    // Don't create new intervals for a register being spilled.
    // The new intervals would have to be spilled anyway so its not worth it.
    // Also they currently aren't spilled so creating them and not spilling
    // them results in incorrect code.
    bool BeingSpilled = false;
    for (unsigned i = 0, e = RegsBeingSpilled.size(); i != e; ++i) {
      if (LI->reg == RegsBeingSpilled[i]) {
        BeingSpilled = true;
        break;
      }
    }

    if (BeingSpilled) continue;

    // LI may have been separated, create new intervals.
    LI->RenumberValues();
    ConnectedVNInfoEqClasses ConEQ(LIS);
    unsigned NumComp = ConEQ.Classify(LI);
    if (NumComp <= 1)
      continue;
    ++NumFracRanges;
    bool IsOriginal = VRM && VRM->getOriginal(LI->reg) == LI->reg;
    DEBUG(dbgs() << NumComp << " components: " << *LI << '\n');
    SmallVector<LiveInterval*, 8> Dups(1, LI);
    for (unsigned i = 1; i != NumComp; ++i) {
      Dups.push_back(&createEmptyIntervalFrom(LI->reg));
      // If LI is an original interval that hasn't been split yet, make the new
      // intervals their own originals instead of referring to LI. The original
      // interval must contain all the split products, and LI doesn't.
      if (IsOriginal)
        VRM->setIsSplitFromReg(Dups.back()->reg, 0);
      if (TheDelegate)
        TheDelegate->LRE_DidCloneVirtReg(Dups.back()->reg, LI->reg);
    }
    ConEQ.Distribute(&Dups[0], MRI);
    DEBUG({
      for (unsigned i = 0; i != NumComp; ++i)
        dbgs() << '\t' << *Dups[i] << '\n';
    });
  }

static bool isPotentiallyReachableInnerNotViaDef(const BasicBlock *DefBB, SmallVectorImpl<BasicBlock *> &Worklist, const BasicBlock *SpBB,
                                        std::set<BasicBlock*>& EndBlocks,
                                        const DominatorTree *DT,
                                        const LoopInfo *LI) {

  // we can not conservatively include the use when timeout
  SmallSet<const BasicBlock*, 64> Visited;

  do {
    // This is a depth-first search for a path not via def
    // return true whenever the first valid path is found
    BasicBlock *BB = Worklist.pop_back_val();

    // if has already visited
    if (!Visited.insert(BB))
      continue;

    // Here we have 3 cases:
    // 1. If BB == SpBB, we just start the search from safepoint, and def should before safepoint in the same block, and BB == DefBB does not mean we reach the def in the search path.
    // 2. If DefBB == StopBB, it infers that use is a phi otherwise this case would be returned in a fastpath in isPotentiallyReachableNotViaDef().
    // and if use is a phi and in the same block with def, we reach use before def.
    // However, this case could not happen because if use is phi, it will stop at one of its incoming block and return true.
    // 3. If only BB == DefBB, we reach the def in the search path and this path should be discarded.
    if (BB == DefBB && BB != SpBB)
      continue;

    if (EndBlocks.find(BB) != EndBlocks.end())
      return true;

#ifdef OPTIMIZED_LIVENESS_ANALYSIS
    // If curent basicblock, the defblock, and any incoming block of PhiNode are not within a loop,
    // we can strip the loop and only add the loop exsit basicblock into the worklist to make the search shorter
    if (LI && (DefBB == NULL || !loopContainsBoth(LI, BB, DefBB))) {
      bool contains = false;
      for (std::set<BasicBlock*>::iterator itr = EndBlocks.begin(), end = EndBlocks.end(); itr != end; itr++) {
        if (loopContainsBoth(LI, BB, *itr)) {
          contains = true;
          break;
        }
      }
      if (!contains) {
        if (const Loop *Outer = getOutermostLoop(LI, BB)) {
          // All blocks in a single loop are reachable from all other blocks. From
          // any of these blocks, we can skip directly to the exits of the loop,
          // ignoring any other blocks inside the loop body.
          Outer->getExitBlocks(Worklist);
        }
      } else {
        Worklist.append(succ_begin(BB), succ_end(BB));
      }
    } else {
      Worklist.append(succ_begin(BB), succ_end(BB));
    }
#else
    Worklist.append(succ_begin(BB), succ_end(BB));
#endif
  } while (!Worklist.empty());

  // We have exhausted all possible paths and are certain that 'To' can not be
  // reached from 'From'.
  return false;
}

void LiveRangeEdit::eliminateDeadDefs(SmallVectorImpl<MachineInstr*> &Dead,
                                      ArrayRef<unsigned> RegsBeingSpilled) {
  SetVector<LiveInterval*,
            SmallVector<LiveInterval*, 8>,
            SmallPtrSet<LiveInterval*, 8> > ToShrink;

  for (;;) {
    // Erase all dead defs.
    while (!Dead.empty()) {
      MachineInstr *MI = Dead.pop_back_val();
      assert(MI->allDefsAreDead() && "Def isn't really dead");
      SlotIndex Idx = LIS.getInstructionIndex(MI).getRegSlot();

      // Never delete inline asm.
      if (MI->isInlineAsm()) {
        DEBUG(dbgs() << "Won't delete: " << Idx << '\t' << *MI);
        continue;
      }

      // Use the same criteria as DeadMachineInstructionElim.
      bool SawStore = false;
      if (!MI->isSafeToMove(&TII, 0, SawStore)) {
        DEBUG(dbgs() << "Can't delete: " << Idx << '\t' << *MI);
        continue;
      }

      DEBUG(dbgs() << "Deleting dead def " << Idx << '\t' << *MI);

      // Check for live intervals that may shrink
      for (MachineInstr::mop_iterator MOI = MI->operands_begin(),
             MOE = MI->operands_end(); MOI != MOE; ++MOI) {
        if (!MOI->isReg())
          continue;
        unsigned Reg = MOI->getReg();
        if (!TargetRegisterInfo::isVirtualRegister(Reg))
          continue;
        LiveInterval &LI = LIS.getInterval(Reg);

        // Shrink read registers, unless it is likely to be expensive and
        // unlikely to change anything. We typically don't want to shrink the
        // PIC base register that has lots of uses everywhere.
        // Always shrink COPY uses that probably come from live range splitting.
        if (MI->readsVirtualRegister(Reg) &&
            (MI->isCopy() || MOI->isDef() || MRI.hasOneNonDBGUse(Reg) ||
             LI.killedAt(Idx)))
          ToShrink.insert(&LI);

        // Remove defined value.
        if (MOI->isDef()) {
          if (VNInfo *VNI = LI.getVNInfoAt(Idx)) {
            if (TheDelegate)
              TheDelegate->LRE_WillShrinkVirtReg(LI.reg);
            LI.removeValNo(VNI);
            if (LI.empty()) {
              ToShrink.remove(&LI);
              eraseVirtReg(Reg);
            }
          }
        }
      }

      if (TheDelegate)
        TheDelegate->LRE_WillEraseInstruction(MI);
      LIS.RemoveMachineInstrFromMaps(MI);
      MI->eraseFromParent();
      ++NumDCEDeleted;
    }

    if (ToShrink.empty())
      break;

    // Shrink just one live interval. Then delete new dead defs.
    LiveInterval *LI = ToShrink.back();
    ToShrink.pop_back();
    if (foldAsLoad(LI, Dead))
      continue;
    if (TheDelegate)
      TheDelegate->LRE_WillShrinkVirtReg(LI->reg);
    if (!LIS.shrinkToUses(LI, &Dead))
      continue;
    
    // Don't create new intervals for a register being spilled.
    // The new intervals would have to be spilled anyway so its not worth it.
    // Also they currently aren't spilled so creating them and not spilling
    // them results in incorrect code.
    bool BeingSpilled = false;
    for (unsigned i = 0, e = RegsBeingSpilled.size(); i != e; ++i) {
      if (LI->reg == RegsBeingSpilled[i]) {
        BeingSpilled = true;
        break;
      }
    }
    
    if (BeingSpilled) continue;

    // LI may have been separated, create new intervals.
    LI->RenumberValues(LIS);
    ConnectedVNInfoEqClasses ConEQ(LIS);
    unsigned NumComp = ConEQ.Classify(LI);
    if (NumComp <= 1)
//.........这里部分代码省略.........